C H A P T E R

4
Urinalysis
Giovanni B. Fogazzi and Giuseppe Garigali

DEFINITION occasionally be necessary. In special situations, urine can also be

collected through a bladder catheter, although the catheter may
Urinalysis is one of the key tests to evaluate kidney and urinary tract cause hematuria. Permanent indwelling catheters are often associ-
disease. When a patient is first seen by a nephrologist, urinalysis ated with bacteriuria, leukocyturia, hematuria, and candiduria.
should always be performed. Dipsticks are the most widely used The container for urine should be provided by the laboratory or
method for urinalysis, but the nephrologist should be aware of their bought in a pharmacy. It should be clean, have a capacity of at least
limitations. Urine sediment examination is an integral part of uri- 50 to 100 ml, and have a diameter opening of at least 5 cm to allow
nalysis, which is performed routinely in general clinical laboratories. easy collection. It should have a wide base to avoid accidental spillage
Ideally, however, urine microscopy should be performed by trained and should be capped. The label should identify the patient as well
nephrologists rather than clinical laboratory personnel, who are at as the hour of urine collection.
times unable to identify important elements,1 and who are not always Several elements (but especially leukocytes) can lyse rapidly after
aware of the clinical correlates of the findings.2 collection, thus ideally the sample should be handled and examined
This chapter describes the main aspects of urinalysis, including as soon as possible. In everyday practice, we suggest the samples be
urine collection, evaluation of physical and chemical features of analyzed within 3 hours from collection. If this is not possible, refrig-
urine, and urine microscopy. eration of specimens at +4° to +8° C assists preservation but may
cause precipitation of phosphates or urates, which can hamper exam-
ination. Alternatively, chemical preservatives such as formaldehyde
URINE COLLECTION or glutaraldehyde can be used.

The way urine is collected and handled can greatly influence the
results (Box 4-1). Written instructions for performing a urine col- PHYSICAL CHARACTERISTICS
lection should be given to the patient. First, strenuous physical exer-
cise (e.g., running, soccer) should be avoided for at least 24 hours Color
before the collection to avoid exercise-induced proteinuria and The color of normal urine ranges from pale to dark yellow and
hematuria or cylindruria. In women, urinalysis should also be amber, depending on the concentration of the urochrome. Abnormal
avoided during menstruation because blood contamination can changes in color can be caused by pathologic conditions, drugs, or
easily occur. foods.
If a midstream sample of the first morning urine is used, lysis of The most frequent pathologic conditions that can cause color
cells and casts may occur in the bladder overnight, which may lead changes of the urine are gross hematuria, hemoglobinuria, or myo-
to false-negative results at urine sediment examination. For this globinuria (pink, red, brown, or black urine); bilirubinuria (dark-
reason, for renal patients, we suggest performing a combined dip- yellow to brown urine); and massive uric acid crystalluria (pink
stick and urine microscopy on the second morning urine. urine). Less frequent causes are urinary infection, mainly from Kleb-
For the measurement of 24-hour protein excretion, a 24-hour siella spp., Proteus mirabilis, Escherichia coli, Providencia stuartii,
urine collection is needed. Errors caused by improper timing and or Enterococcus spp. in patients with permanent bladder catheter
missed samples can lead to overcollection or undercollection of (purple urine, sometimes called “purple urine bag syndrome”)4; chy-
urine. Errors can be minimized by giving the patient simple written luria (white milky urine); and porphyrinuria (associated with the
instructions. Written instructions should also be provided for other excretion in the urine of porphobilinogen) and alkaptonuria (red
types of urine collection, such as that needed for the evaluation of urine turning black on standing).
orthostatic proteinuria, which implies the collection of one sample The main drugs responsible for abnormal urine color are rifampin
produced while the patient has been recumbent for some hours, and (yellow-orange to red urine); desferrioxamine (pinkish urine); phe-
another sample produced while the patient has been standing. nytoin (red urine); chloroquine and nitrofurantoin (brown urine);
Spot urine samples are widely recommended3 because they are triamterene, propofol, and blue dyes of enteral feeds (green urine);
easy to obtain, although timed urines are still recommended by some methylene blue (blue urine); and metronidazole, methyldopa, and
authorities (see Chapter 80). imipenem-cilastatin (darkening on standing).
After the washing of hands, women should spread the labia of the Among foods are beetroot (red urine), senna and rhubarb (yellow
vagina and men withdraw the foreskin of the glans. The external to brown or red urine), and carotene (brown urine).
genitalia are washed and wiped dry with a paper towel, and the
“midstream” urine is collected after the first portion is discarded. The
same procedures can also be used for children. For small infants, Turbidity
bags for urine are often used, even though these carry a high Normal urine is transparent. Urine can be turbid because of a high
probability of contamination. A suprapubic bladder puncture may concentration of any urine particle, especially cells, crystals, and
39
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40 SECTION II Investigation of Renal Disease

number of solutes per unit volume and measures all solutes rather
Procedures for Preparation and Examination than just ionic substances. Therefore, refractometry is more accurate
of Urine Sediment than dipstick, despite being influenced by urine temperature,
Written instructions to the patients for urine collection.
although temperature-compensated refractometers are available.
Refractometers are inexpensive, simple to use, and have the major
Collection in disposable containers of the second urine of the
morning after discarding the first few milliliters of urine (i.e., advantage of requiring only 1 drop of urine. For these reasons, we
midstream urine). suggest the use of refractometry for everyday practice.
Sample handling and examination within 3 hours of collection. An SG of 1.000 to 1.003 is consistent with marked urinary dilu-
Centrifugation of a 10-ml aliquot of urine at 400 g for 10 minutes. tion, as observed in patients with diabetes insipidus or water intoxi-
Removal by suction of 9.5 ml of supernatant urine.
cation. SG of 1.010 is often called isosthenuric urine because it is of
similar SG (and osmolality) to plasma, so it is often observed in
Gentle but thorough resuspension with a Pasteur pipette of
sediment in remaining 0.5 ml of urine. conditions in which urinary concentration is impaired, such as acute
Transfer by a precision pipette of 50 µl of resuspended urine to
tubular necrosis (ATN) and chronic kidney disease. SG above 1.040
a slide. almost always indicates the presence of some extrinsic osmotic
Covering of sample with a 24 × 32–mm coverslip. agent, such as radiocontrast.
Examination of the urine sediment by a phase contrast
Osmolality is measured by an osmometer, which evaluates the
microscope at ×160 and ×400. freezing-point depression of a solution and supplies results as mil-
Use of polarized light to identify suspected lipids and crystals. liosmoles per kilogram (mOsm/kg) of water. Osmolality depends
Matching of the microscopic findings with dipstick for pH,
only on the number of particles present and is not influenced by
specific gravity, hemoglobin, leukocyte esterase, nitrites, and urine temperature or protein concentrations. However, high glucose
albumin (presence of albumin orients examination of sample concentrations significantly increase osmolality (10 g/l of glucose =
toward a glomerular disease). 55.5 mOsm/l). The measurement of osmolality is more reliable than
Cells expressed as lowest/highest number seen per high-power SG by either dipstick or refractometry for the evaluation of patho-
field (hpf), casts as number per low-power field (lpf), and all logic urine.
other elements (e.g., bacteria, crystals) on scale from 0 to
++++.

Box 4-1 Preparation and examination of urine sediment. Procedures CHEMICAL CHARACTERISTICS
used in the authors’ laboratory.
Chemical characteristics of urine are most frequently evaluated by
bacteria. The most frequent causes of turbidity are urinary tract dipstick. Dipsticks have the advantages of simplicity, low cost, and
infection, heavy hematuria, and contamination of urine from genital stability. Disadvantages include qualitative or semiquantitative
secretions. The absence of turbidity is not a reliable criterion by results only, susceptibility to interference by substances, and urine
which to judge a urine sample because pathologic urine can be discoloration. When the reading is visual and not by automated
transparent. instruments, the interval between removal of the dipstick from urine
and the reading of results indicated by the manufacturer must be
respected to avoid false results.
Odor Sensitivity and specificity of dipsticks greatly differ among studies
A change in urine odor may be caused by the ingestion of some and depend on the brand used and different clinical conditions and
foods, such as asparagus. A pungent odor, caused by the production patient populations investigated. False results can also be caused by
of ammonia, is typical of most bacterial urinary tract infection, the use of time-expired dipsticks. Table 4-1 summarizes the main
whereas there is often a sweet or fruity odor with ketones in the false-negative and false-positive results that can occur with urine
urine. Some rare conditions confer a characteristic odor to the urine. dipstick testing.
These include maple syrup urine disease (maple syrup odor), phe-
nylketonuria (musty or mousy odor), isovaleric acidemia (sweaty
feet odor), and hypermethioninemia (rancid butter or fishy odor). pH
The pH is determined by dipsticks that cover the pH range of 5.0 to
8.5 or to 9.0. With use of dipsticks, significant deviations from true
Relative Density pH are observed for values below 5.5 and above 7.5. Therefore, a pH
The relative density parameter can be measured by specific gravity meter with a glass electrode is mandatory if an accurate measure-
or osmolality. Specific gravity (SG) refers to the weight of a volume ment is necessary.
of urine compared with the weight of the same volume of distilled Urine pH reflects the presence of hydrogen ions (H+), but this
water and depends on the mass and number of the dissolved parti- does not necessarily reflect the overall acid load in the urine because
cles. SG is most frequently evaluated by dipstick, which measures the most of the acid is excreted as ammonia. A low pH is often observed
ionic concentration of urine. In the presence of ions, protons are with metabolic acidosis (in which acid is secreted), with high-protein
released by a complexing agent and produce a color change in the meals (which generate more acid and ammonia), and with volume
indicator bromthymol blue from blue to blue-green to yellow. Under- depletion (in which aldosterone is stimulated, resulting in an acid
estimation occurs with urine pH above 6.5, whereas overestimation urine). Indeed, low urine pH may help distinguish pre-renal acute
is found with urine protein concentration above 7.0 g/L. Because kidney injury (AKI) from ATN, which is typically associated with a
nonionized molecules, such as glucose and urea, are not detected by higher pH. High pH is often observed with renal tubular acidosis
dipstick, this method does not strictly correlate with the results (especially distal, type 1; see Chapter 12), with vegetarian diets
obtained by refractometry and osmolality. (caused by minimal nitrogen and acid generation), and with infec-
Refractometry measures SG through the refraction of light while tion with urease-positive organisms (e.g., Proteus) that generate
it passes through a drop of urine on a glass plate. This measures the ammonia from urea.

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 CHAPTER 4 Urinalysis    41

Glucose
Urine Dipstick Testing Glucose is also often detected by dipstick. With glucose oxidase as
False-positive catalyst, glucose is first oxidized to gluconic acid and hydrogen per-
Constituent False-negative Results Results oxide. Through the catalyzing activity of a peroxidase, hydrogen
Specific Urine pH >6.5 Urine protein peroxide then reacts with a reduced colorless chromogen to form a
gravity (SG) >7.0 g/l colored product. This test detects concentrations of 0.5 to 20 g/l.
pH Reduced values in presence — When more precise quantification of urine glucose is needed, enzy-
of formaldehyde matic methods such as hexokinase must be used.
Hemoglobin Ascorbic acid Myoglobin False-negative results with glucose detection occur in the pres-
High SG of urine Microbial ence of ascorbic acid and bacteria. False-positive findings may be
Formaldehyde (0.5 g/l) used peroxidases observed in the presence of oxidizing detergents.
to preserve samples
Glucose Ascorbic acid Oxidizing
Bacteria detergents Protein
Albumin Immunoglobulin light Urine pH ≥9.0 Although there is no consistent definition of proteinuria,7 it is
chains Quaternary accepted that physiologic proteinuria does not exceed 150 mg/24 h
Tubular proteins ammonium for adults and 140 mg/m2 for children. Three different approaches
Globulins detergents
Chlorhexidine can be used for the evaluation of proteinuria, as described next.
Polyvinylpyrrolidone
Leukocyte Glucose ≥20.0 g/l Formaldehyde
Albumin Dipstick
esterase Protein >5.0 g/l (0.4 g/l) The albumin dipstick test is based on the presence of protein in a
Cephalothin (+++) ?Imipenem buffer causing a change in pH proportional to the concentration of
Tetracycline (+++) ?Meropenem protein itself. The dipstick changes its color, from pale green to green
Cephalexin (++) ?Clavulanate and blue, according to the pH changes induced by the protein. The
Tobramycin (+) Abnormally colored
High SG of urine urine dipstick for protein is sensitive to albumin but has a very low sensi-
tivity to other proteins, such as tubular proteins and light-chain
Nitrites Bacteria that do not reduce Abnormally colored
nitrates to nitrites urine
immunoglobulins; thus the dipstick will not detect the overflow pro-
No vegetables in diet teinuria that can occur in myeloma. Moreover, the detection limit is
Short bladder incubation 0.25 to 0.3 g/l, which may be too high to identify the early phases of
time kidney disease (i.e., microalbuminuria) and is influenced by hydra-
Ketones Improper storage Free sulfhydryl tion status (false-negative results may occur at low urine SG, and vice
groups (e.g., versa) and urine pH (false-positive results at strongly alkaline pH).
captopril) Also, dipstick supplies only a semiquantitative measurement of urine
Levodopa
Abnormally colored
albumin, which is expressed on a scale from 0 to +++ or ++++.7 Some
urine manufacturers also supply numerical results, although these repre-
sent only approximate quantitative measurements. Thus, for accurate
Table 4-1 Urine dipstick testing. Main false-negative and false-positive quantification, other methods are needed. Recently, a creatinine test
results of urine dipsticks. False results may also occur when time-expired
dipsticks are used. pad has been added to some dipsticks, which supplies a protein-
creatinine ratio (PCR) and reduces the variability caused by chang-
ing diuresis and urine dilution.8

Measurement of urine pH is also needed for the interpretation of 24-Hour Protein Excretion
urinalysis (see Leukocyte Esterase and Urine Microscopy). The 24-hour urine collection for protein excretion remains the refer-
ence (gold standard) method. It is based on chemical assay (e.g.,
biuret or Folin-Lowry reaction), turbidimetric technique (e.g., tri-
Hemoglobin chloroacetic acid, benzethonium chloride, ammonium chloride), or
Hemoglobin is detected by a dipstick on the basis of the pseudoper- dye-binding technique (e.g., ponceau S, Coomassie brilliant blue
oxidase activity of the heme moiety of hemoglobin, which catalyzes G-250, pyrogallol red molybdate), which quantify total proteins
the reaction of a peroxide and a chromogen to form a colored rather than simply albumin. The 24-hour protein excretion averages
product. The presence of hemoglobin is shown as green spots, which the variation of proteinuria caused by the circadian rhythm and is
result from intact erythrocytes, or as a homogeneous, diffuse green the most accurate for monitoring of proteinuria during treatment.
pattern. This can result from marked hematuria because of the high However, it can be impractical in some settings (e.g., children, out-
number of erythrocytes that cover the whole pad surface; from lysis patients, elderly patients) and is subject to error from overcollection
of erythrocytes favored by delayed examination, alkaline urine pH, or undercollection. For this reason, we give our patients written,
or low SG; or from hemoglobinuria secondary to intravascular simple but definitive instructions on how to collect urine (see earlier
hemolysis. discussion).
False-negative results are mainly caused by (1) ascorbic acid, a
strong reducing agent, which can result in low-grade microscopic Protein-Creatinine Ratio on Random Urine Sample
hematuria being completely missed,5 and (2) high SG. This PCR is obtained by the ratio between urine protein excretion
The most important causes of false-positive results are myoglo- (measured by methods in 24-Hour Protein Excretion) and creatinine
binuria, resulting from rhabdomyolysis, and a high concentration of excretion, expressed as mg/mg or mg/mmol. PCR represents a prac-
bacteria with pseudoperoxidase activity (Enterobacteriaceae, staphy- tical alternative to the 24-hour urine collection because it is easy to
lococci, and streptococci).6 obtain and is not influenced by variation in water intake or rate of

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42 SECTION II Investigation of Renal Disease

diuresis.3 Also, the same sample can also be used for microscopic in patients with monoclonal gammopathies. Bence Jones proteinuria
investigation. is revealed by urine electrophoresis, whereas light-chain identifica-
A close correlation between the PCR in a random urine sample tion requires urine immunofixation.20
and the 24-hour protein excretion has been demonstrated in a wide Selectivity of Proteinuria Selectivity can be assessed in
range of patients,7,9 including those with different types of glomeru- nephrotic patients by the ratio of the clearance of IgG (molecular
lonephritis (GN) evaluated longitudinally during treatment.10 weight of 160,000 d) to the clearance of transferrin (88,000 d).21
However, the results may be influenced by a reduced creatinine Although now used infrequently, highly selective proteinuria (ratio
excretion because of reduced muscle mass. Thus, in elderly and <0.1) in nephrotic children suggests the diagnosis of minimal change
female patients, PCR values can be higher than in young men. disease and predicts corticosteroid responsiveness.
Another factor to be considered is the timing of the sample, which
is influenced by the daily circadian fluctuation of protein excretion
in the presence of minimal corresponding variation of creatinine Leukocyte Esterase
excretion. Thus, the best estimates are probably obtained with The leukocyte esterase dipstick test evaluates the presence of leuko-
morning samples, but not the first void.11 cytes based on the activity of an indoxyl esterase released from lysed
Some consider that a normal PCR is sufficient to rule out patho- neutrophil granulocytes. Leukocyte esterase may be positive when
logic proteinuria, but that an elevated PCR should be confirmed microscopy is negative and when leukocytes are lysed, because of
and quantified with a 24-hour collection.12 Other investigators low relative density, alkaline pH, or a delay in sample handling and
have found poor correlation between PCR and 24-hour proteinuria examination.
at high levels of protein excretion,10 or that PCR is an unreliable False-negative results derive from high glucose (≥20 g/l) or high
method to monitor some patients with lupus nephritis13,14 (see also protein (≥5 g/l) concentration or from the presence of antibiotics
Chapter 80). such as cephalothin and tetracycline (strong inhibition), cephalexin
A possible alternative to PCR is the measurement of albumin- (moderate inhibition), or tobramycin (mild inhibition). The sensitiv-
creatinine ratio (ACR), especially to screen and monitor diabetic ity is also reduced by high SG because this prevents leukocyte lysis.
patients.9 However, with ACR false-negative results may occur,15 as False-positive results may occur when formaldehyde is used as a
a consequence of the variable proportion of albumin present in the urine preservative and, according to one report, from the presence
urine, which may depend on the underlying renal disease. An ele- in the urine of imipenem, meropenem, or clavulanate.22
vated PCR with a negative ACR for example suggests the diagnosis
of myeloma.
The ratio of urinary albumin to total protein excretion (urine Nitrites
albumin/protein ratio, uAPR) has recently been proposed as The dipstick nitrites test detects bacteria that reduce nitrates to
a method to distinguish proteinuric patients with a pure glo- nitrites by nitrate reductase activity. This includes most gram-
merular disease from patients with a glomerular disease associated negative uropathogenic bacteria, but not Pseudomonas, Staphylococ-
with tubulointerstitial damage or with a tubulointerstitial nephrop- cus albus, or Enterococcus. A positive test result also occurs with a
athy. However, uAPR is not yet validated for routine clinical diet rich in nitrates (vegetables), which form the substrate for nitrite
practice.16,17 production, and sufficient bladder incubation time. Thus, not sur-
prisingly, the sensitivity of the dipstick nitrites test is low, but speci-
Specific Proteins ficity is high.23
Microalbuminuria Defined as the presence of albumin in the urine
in a range of 30 to 299 mg/24 h, microalbuminuria identifies diabetic
patients at increased risk of developing overt diabetic nephropathy. Bile Pigments
Also, in the general population, microalbuminuria identifies patients Measurement of urinary urobilinogen and bilirubin concentrations
at increased risk of chronic kidney disease, cardiovascular morbidity, has lost its clinical value in the detection of liver disease after the
and overall mortality. The 24-hour urine collection, initially consid- introduction of serum tests of liver enzyme function.
ered the gold standard method for the detection of microalbumin-
uria, currently has been replaced by the use of early-morning urine,
which minimizes the changes caused by diurnal volume variations. Ketones
A number of semiquantitative dipstick tests are available to screen The ketone dipstick tests for acetoacetate and acetone (but not
for microalbuminuria. β-hydroxybutyrate), which are excreted into urine during diabetic
Once microalbuminuria is found by dipstick, a standard quantita- acidosis or during fasting, vomiting, or strenuous exercise. It is based
tive method is then used for confirmation, usually immunoassay.18 on the reaction of the ketones with nitroprusside.
Because of its great simplicity, immunoturbidometry is the method
most frequently used.
Tubular Proteins Low-molecular-weight tubular proteins such URINE MICROSCOPY
as α1-microglobulin, retinol-binding protein, and β2-microglobulin
are identified by a qualitative analysis of urine proteins, using elec- Methods
trophoresis on cellulose acetate or agarose after protein concentra- The second urine specimen of the morning should be collected
tion or using very sensitive stains such as silver and gold. Sodium because it avoids the lysis of particles that can occur in the bladder
dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) can overnight (see Urine Collection and Box 4-1). We centrifuge an
be used to identify tubular proteins in the urine of patients with aliquot of urine within 3 hours from collection and concentrate it by
glomerular diseases, which may have therapeutic and prognostic removal of a fixed aliquot of supernatant urine. After this, the sedi-
implications.19 ment is resuspended with a Pasteur pipette, and a fixed aliquot is
Bence Jones Proteinuria The Bence Jones protein indicates the transferred to the slide and prepared using a coverslip with a fixed
presence in the urine of free immunoglobulin light chains, as occurs surface.

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 CHAPTER 4 Urinalysis    43

Phase contrast microscopy is recommended because it improves interstitial nephritis. Neutrophils can be found in low numbers in
the identification of almost all particles, whereas polarized light is chronic interstitial nephritis and in proliferative GN, intermingled
mandatory for the correct identification of some lipids and crystals.24 with high numbers of erythrocytes.29
At least 20 microscopic fields, in different areas of the sample, should Eosinophils, which can be identified only by the use of stains (e.g.,
be examined at both low magnification (e.g., ×100 or ×200) and high Hansel), were once considered a marker of acute allergic interstitial
magnification (e.g., ×400). More extensive examination may be nephritis. Currently, however, eosinophils are seen as nonspecific
required in certain clinical settings, such as isolated microhematuria because they may be present in various types of GN, prostatitis,
of unknown origin, for which we suggest examination of 50 low- chronic pyelonephritis, urinary schistosomiasis, and cholesterol
power fields (lpf) to look for erythrocyte casts. embolism (see Chapter 66).30,31
For correct examination, both pH and SG of the sample should Lymphocytes, whose identification also requires staining of the
be known. Both alkaline pH (≥7.0) and low SG (especially <1.010) sample, may indicate acute cellular rejection in renal allograft recipi-
favor the lysis of erythrocytes and leukocytes, which can cause dis- ents. However, finding lymphocytes in the urine cannot replace more
crepancies between dipstick readings and the microscopic examina- reliable diagnostic tools such as renal biopsy. Lymphocytes are also
tion (see earlier discussion). Alkaline pH also impairs the formation a typical finding in patients with chyluria.
of casts and favors the precipitation of phosphates. Macrophages are mononucleated or multinucleated cells of vari-
The various elements observed are quantified as number per able size (13 to 95 µm in diameter) and variable appearance: granu-
microscopic field, and if counting chambers are used, the elements lar (Fig. 4-1, D), vacuolar, phagocytic (when cytoplasm contains
are quantified as number per milliliter. Counting chambers allow a bacterial debris, cell fragments, destroyed erythrocytes, crystals,
precise quantitation but are rarely used in everyday practice. etc.), or homogeneous (when cytoplasm does not contain granules
or other particles). In patients with the nephrotic syndrome, macro-
phages may be engorged with lipid droplets, appearing as “oval fat
Cells bodies.”32 Macrophages have been found in the urine of patients with
Erythrocytes active GN. In our experience, macrophages are frequently seen in
Urinary erythrocytes have a diameter of 4 to 10 µm. In the urine, the urine of kidney transplant recipients with BK virus infection (see
there are two main types of erythrocytes: isomorphic, with regular later discussion). However, urinary macrophages are not yet consid-
shapes and contours, derived from the urinary excretory system; and ered diagnostic of any specific condition.
dysmorphic, with irregular shapes and contours, which are of glo-
merular origin (Fig. 4-1, A and B).25 Thus, according to the propor- Renal Tubular Epithelial Cells
tion of isomorphic and dysmorphic erythrocytes found in the The renal tubular epithelial cells (RTECs) derive from the exfoliation
sample, hematuria is defined as nonglomerular or glomerular. of the tubular epithelium. In the urine, RTECs can differ in size
Unfortunately, there is no agreement on the criteria to use for such (diameter ~9 to 25 µm) and shape, from roundish to rectangular or
classification. Some authors define glomerular hematuria as more columnar, with a central or peripheral large nucleus (Fig. 4-1, E).
than 80% of erythrocytes being dysmorphic; others define the dis- RTECs are not found in the normal individual but can be found in
criminating cutoff as being as low as 10% or 14%.24 Still others define all patients with conditions associated with acute tubular damage,
hematuria as glomerular when at least 5% of erythrocytes examined such as ATN,33 acute interstitial nephritis, and acute cellular rejec-
are acanthocytes,26 a subtype of dysmorphic erythrocytes with a dis- tion of a renal allograft. In smaller numbers, RTECs can also be
tinguishing appearance easily identifiable by the presence of one or found in glomerular diseases.29 In ATN, these cells are frequently
more blebs of different size and shape protruding from a ring-shaped damaged and necrotic and may be present in casts (so-called epithe-
body (Fig. 4-1, B, inset). lial casts).
In our laboratory, glomerular hematuria is diagnosed when there
are 40% or more dysmorphic erythrocytes and/or 5% or more acan- Transitional Epithelial Cells
thocytes and/or one or more red blood cell casts/50 lpf (×160). With The transitional epithelial cells derive from the exfoliation of the
this criterion, a good correlation was found between urinary sedi- uroepithelium, which lines the urinary tract from calyces to the
ment and renal biopsy findings in 16 patients with longstanding bladder in women and to the proximal urethra in men. This multilay-
isolated microhematuria.27 ered epithelium has small cells in the deep layers and larger cells in
Erythrocyte dysmorphism is thought to result from deformation the superficial layers. When present in large numbers (e.g., ≥1/high-
of the erythrocytes as they pass through gaps in the glomerular power field [hpf]), cells of the deep epithelial layers (diameter ~10 to
basement membrane, followed by physicochemical insults occur- 38 µm; Fig. 4-1, F) suggest severe damage of uroepithelium, as caused
ring while the erythrocytes pass through the tubular system.28 by neoplasia, stones, obstruction, or longstanding bladder catheters
The distinction between glomerular and nonglomerular hematu- or ureteral stents.24 Transitional cells of the superficial layers (diam-
ria is of special value in the evaluation of patients with isolated eter ~17 to 43 µm; Fig. 4-1, G) are a common finding, being associ-
microhematuria. In these patients, it is important to decide from the ated with mild damage of uroepithelium, as may occur in cystitis.
early phases of the diagnostic workup whether nephrologic or uro-
logic investigation is needed. Squamous Epithelial Cells
The squamous epithelial cells (diameter, 17 to 118 µm; Fig. 4-1, H)
Leukocytes derive from the urethra or from the external genitalia. In small
Urinary neutrophils range from 7 to 15 µm in diameter and are the numbers, squamous cells are a normal finding, but in large numbers,
most frequently found leukocytes in the urine. Neutrophils are iden- they indicate urine contamination from genital secretions.
tified by their granular cytoplasm and lobulated nucleus (Fig. 4-1,
C). In most patients, neutrophils indicate lower or upper urinary
tract infection, but they may also result from urine contamination Lipids
caused by genital secretions, especially in young women. Variable Lipids are found in the urine as drops, which are spherical, translu-
numbers of neutrophils are often, but not always, found in acute cent, yellowish particles of different size that can be isolated or in

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44 SECTION II Investigation of Renal Disease

A B

E G H
Figure 4-1 Urinary sediment cells. A, Isomorphic nonglomerular erythrocytes. The arrows indicate the so-called crenated erythrocytes, which are a finding
in nonglomerular hematuria. B, Dysmorphic glomerular erythrocytes. The dysmorphism consists mainly of irregularities of the cell membrane. Inset, Acan-
thocytes, with their typical ring-formed cell bodies with one or more blebs of different sizes and shapes. C, Neutrophils. Note their typical lobulated nucleus
and granular cytoplasm. D, Granular phagocytic macrophage (diameter ~60 µm). E, Different types of renal tubular epithelial cells. F, Two cells from deep
layers of uroepithelium. G, Three cells from superficial layers of uroepithelium. Note the difference in shape, size, and ratio of nucleus to cytoplasm between
the two types of uroepithelial cells. H, Squamous epithelial cells. (All images by phase contrast microscopy; original magnification ×400.)

clusters (Fig. 4-2, A); as oval fat bodies, which are RTECs or macro- from those previously described because they contain glycosphingo-
phages gorged with lipid droplets32; as fatty casts, cylindrical struc- lipids (especially globotriaosylceramide-3) and have irregular shape
tures containing variable amounts of fatty droplets or even oval fat and size, variable protrusions or an internal lamellar structure, and
bodies; and cholesterol crystals (see Crystals). All these particles irregular or truncated Maltese crosses under polarized light (Fig. 4-2,
contain mainly cholesterol esters and free cholesterol and under C). It has recently been demonstrated that these fatty particles are of
polarized light have the appearance of Maltese crosses with sym- diagnostic importance.34
metric arms (Fig. 4-2, B).
These lipids are typical of glomerular diseases associated with
marked proteinuria, usually but not invariably in the nephrotic Casts
range. Casts are cylindrical structures that form in the lumen of distal
In Fabry disease, urine sediment contains fatty particles even in renal tubules and collecting ducts. Their matrix is made of Tamm-
the absence of proteinuria (see Chapter 48). These particles differ Horsfall glycoprotein, also called uromodulin, which is secreted by

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 CHAPTER 4 Urinalysis    45

A B C
Figure 4-2 Fatty particles. A, Aggregated and isolated (arrows) round lipid droplets by phase contrast microscopy. B, Same lipid droplets in A under
polarized light, showing typical Maltese crosses with symmetric arms. C, Fatty particle with protrusions, as found in Fabry disease (phase contrast microscopy).
Inset, Same particle under polarized light. Note the truncated Maltese cross. (Original magnification ×400.)

■ Hyaline casts are colorless with a low refractive index (Fig. 4-3,
Clinical Significance of Urinary Casts A). They are easily seen with phase contrast microscopy but can
Cast Main Clinical Associations be overlooked when bright-field microscopy is used. Hyaline casts
Hyaline Normal individual; renal disease may occur in normal urine, especially when it is concentrated and
acid (both conditions favoring precipitation of Tamm-Horsfall
Hyaline-granular Normal individual; renal disease
protein). In patients with renal disease, hyaline casts are usually
Granular Renal disease; acute tubular necrosis associated with other types of casts.
Waxy Renal disease with function impairment ■ Hyaline-granular casts contain variable amounts of granules
Fatty Proteinuria; nephrotic syndrome
within the hyaline matrix (Fig. 4-3, B) and are the most common
mixed casts (described later). Hyaline-granular casts are rare in
Erythrocyte Glomerular hematuria; proliferative/
necrotizing GN
normal individuals but are common in patients with renal dis-
eases such as GN29 and acute interstitial nephritis.35
Leukocyte Acute interstitial nephritis; acute ■ Granular casts can be finely granular (Fig. 4-3, C) or coarsely
pyelonephritis; proliferative GN
granular. Both types are typical of renal disease. Recent studies
Renal tubular Acute tubular necrosis; acute interstitial have demonstrated that granular casts together with RTECs33,36 or
epithelial cell nephritis; proliferative GN; nephrotic
(so-called syndrome
with epithelial casts37 are a sensitive marker of ATN.
epithelial casts) ■ Waxy casts derive their name from their appearance, which is
similar to that of melted wax (Fig. 4-3, D). They are typically
Hemoglobin Same as for erythrocyte cast; hemoglobinuria
caused by intravascular hemolysis found in patients with renal disease associated with renal impair-
ment, whether acute, rapidly progressive, or chronic.
Myoglobin Rhabdomyolysis
■ Fatty casts contain variable amounts of lipid droplets, isolated, in
Bilirubin Jaundice caused by increased direct bilirubin clumps, or packed, or even oval fat bodies or cholesterol crystals.
Bacterial, fungal Bacterial or fungal infection in the kidney Fatty casts are typical of glomerular diseases associated with
Containing Normal individual; renal stone disease; marked proteinuria or the nephrotic syndrome.
crystals crystalluric AKI ■ Erythrocyte casts may contain a few erythrocytes (Fig. 4-3, E) or
Mixed According to components present in the cast
so many that the matrix of the cast cannot be identified. Erythro-
cyte casts are usually considered a marker of glomerular bleeding,
Table 4-2 Types of casts and their main clinical associations. even though a recent report found them in 28% of patients with
GN, Glomerulonephritis; AKI, acute kidney injury. acute interstitial nephritis.35
■ Hemoglobin casts have a brownish hue and usually a coarsely
granular appearance, which derives from the degradation of
the cells of the thick ascending limb of Henle loop. Trapping of erythrocytes entrapped within the cast matrix (Fig. 4-3, F). There-
particles within the cast matrix results in casts with different appear- fore, hemoglobin casts have the same clinical significance
ances, each of which may have specific clinical significance (Table as erythrocyte casts. Hemoglobin casts may also derive from
4-2). Because casts form in the renal tubules, whatever particle is hemoglobinuria, as may occur in intravascular hemolysis from
contained in a cast derives from the kidneys. Specific casts include any cause. In these patients, hemoglobin casts have a smooth
the following: surface.

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 A B C D

E F G

H I
Figure 4-3 Casts. A, Hyaline cast. B, Hyaline-granular cast. C, Finely granular cast. D, Waxy cast. E, Erythrocyte cast, with erythrocytes (arrows) plunged
into the cast matrix. F, Hemoglobin cast with a coarsely granular appearance and typical brownish hue. G, Leukocyte cast. Note the lobulated nucleus of
polymorphonuclear leukocytes (arrows). H, Epithelial cell cast. Note the large nucleus of the renal tubular epithelial cells. I, Bilirubin cast with a coarsely
granular appearance and typical yellow color. (All images by phase contrast microscopy; original magnification ×400.)

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 CHAPTER 4 Urinalysis    47

■ Leukocyte casts contain variable amounts of polymorphonuclear Calcium phosphate crystals precipitate in alkaline urine (pH ≥7.0)
leukocytes (Fig. 4-3, G). They can be found in patients with acute and, with the exception of plates, polarize light intensely.
pyelonephritis and acute interstitial nephritis, but are rare in Amorphous phosphates are tiny particles identical to amorphous
GN.29 urates, but these phosphates precipitate at a pH of 7.0 or higher and
■ Renal tubular epithelial cell casts (so-called epithelial casts) contain do not polarize light.
variable numbers of RTECs, which can be identified by their Struvite (Triple Phosphate) Crystals Struvite crystals contain
prominent nucleus (Fig. 4-3, H). Epithelial casts indicate damage magnesium ammonium phosphate and typically have the appear-
of the renal tubular epithelium and can therefore be found in the ance of “coffin lids” (Fig. 4-4, E). Triple phosphate crystals are found
urine of patients with ATN,37 acute interstitial nephritis, and even in alkaline urine (pH ≥7.0) and almost always polarize light strongly.
glomerular disease.29
■ Myoglobin casts are pigmented cylinders, with the myoglobin pro- Pathologic Crystals
viding their color. They may be similar to hemoglobin casts (Fig. Cholesterol Crystals Cholesterol crystals are thin, transparent
4-3, F), from which myoglobin casts can be distinguished by the plates, often clumped together, with sharp edges (Fig. 4-4, F).
clinical setting. Myoglobin casts are observed in the urine of Cystine Crystals Cystine crystals occur in patients with cystin-
patients with AKI associated with rhabdomyolysis. uria and are hexagonal plates with irregular sides that are often
■ Bilirubin casts are cylinders pigmented with bilirubin, which can heaped on one another (Fig. 4-4, G). They precipitate in acid urine.
stain any particle contained in the cast (Fig. 4-3, I). They are Evaluation of their size can be used to predict the recurrence of
observed in the urine of patients with jaundice associated with cystine stones.38
increased direct (conjugated) bilirubin. 2,8-Dihydroxyadenine Crystals These spherical, brownish
■ Casts containing microorganisms (bacteria and yeasts) indicate crystals have a central umbilicus and a birefringent cross-like appear-
renal infection. ance under polarized light (Fig. 4-4, H).39 2,8-Dihydroxyadenine
■ Casts containing crystals indicate that crystals derive from crystals are a marker of homozygotic deficiency of the enzyme
the renal tubules. Crystal casts are an important diagnostic adenine phosphoribosyltransferase. This rare condition causes crys-
element in crystalluric forms of AKI, such as acute urate talluria in about 96% of untreated patients, who frequently also
nephropathy. have radiolucent urinary stone formation, AKI, or chronic kidney
■ Mixed casts contain components of different nature, such as disease.39,40
granules, cells, and lipids. This causes the appearance of pleo- Other rare pathologic crystals are tyrosine, found in patients with
morphic cylinders, whose clinical significance is the same as that acute liver disease and the rare hereditary disease tyrosinemia, and
for the pure types of casts, of which mixed casts contain some leucine, found in acute liver disease.
components.
Crystals Caused by Drugs
Many drugs can cause crystalluria, especially in a setting of drug
Crystals overdose, dehydration, or hypoalbuminemia in the presence of a
Correct identification of urine crystals requires knowledge of crystal specific urinary pH favoring drug crystallization. Examples include
morphology, urine pH, and appearance under polarizing light. the antibiotics sulfadiazine, amoxicillin (Fig. 4-4, I), and ciprofloxa-
Examination of the urine for crystals is informative in the assessment cin (Fig. 4-4, J)24; the antiviral agents acyclovir and indinavir (Fig.
of patients with stone disease, with some rare inherited metabolic 4-4, K); the vasodilators pyridoxylate and naftidrofuryl oxalate; the
disorders (e.g., cystinuria, oxalosis, phosphoribosyltransferase defi- barbiturate primidone; the antiepileptic felbamate; the inhibitor of
ciency), and with suspected drug nephrotoxicity.24 Crystals can be gastroenteric lipase orlistat; and intravenous vitamin C.24 Most of
classified in four categories: common, pathologic, caused by drugs, these drugs cause crystals that are made of the drug itself, with
and other crystals. unusual morphologies that differ from those of the crystals previ-
ously described. However, naftidrofuryl oxalate, orlistat, and vitamin
Common Crystals C cause calcium oxalate crystals, which are indistinguishable from
Uric Acid Crystals and Amorphous Urates Uric acid crystals have calcium oxalate crystals resulting from other causes.
an amber color and a wide spectrum of appearances, including
rhomboids and barrels (Fig. 4-4, A). These crystals are found only in Other Crystals
acid urine (pH 5.0 to 5.8) and are polychromatic under polarizing Hippuric acid crystals, calcium carbonate crystals, and ammonium
light. biurate crystals are rare and devoid of clinical significance.
Amorphous urates are tiny granules of irregular shape that also
precipitate in acid urine. They are identical to amorphous phos- Clinical Significance of Crystals
phates, which, however, precipitate in alkaline urine. In addition, Uric acid, calcium oxalate, and calcium phosphate (brushite) crystals
whereas uric acid crystals polarize light, phosphates do not. may have no clinical significance because they can reflect transient
Calcium Oxalate Crystals There are two types of calcium supersaturation of the urine caused by ingestion of some foods (e.g.,
oxalate crystals: bihydrated (or weddellite) crystals, which most meat for uric acid, spinach or chocolate for calcium oxalate, milk or
often have a bipyramidal appearance (Fig. 4-4, B), and monohy- cheese for calcium phosphate) or mild dehydration. However, the
drated (or whewellite) crystals, which are ovoid, dumbbell shaped, persistence of calcium oxalate or uric acid crystalluria may reflect
or biconcave disks (Fig. 4-4, C). Both types of calcium oxalate crys- hypercalciuria, hyperoxaluria, or hyperuricosuria. In calcium stone
tals precipitate at pH 5.4 to 6.7. Monohydrated crystals always polar- formers, the evaluation of crystalluria may be used to assess calcium
ize light, whereas bihydrated crystals usually do not. stone disease activity.41
Brushite (Calcium Phosphate Crystals) and Amorphous Phos- Large numbers of uric acid crystals may be associated with AKI
phates Brushite crystals are pleomorphic, appearing as prisms, caused by acute urate nephropathy, whereas large numbers of mono-
star-like particles, or needles of various sizes and shapes (Fig. 4-4, hydrated calcium oxalate crystals, especially with a spindle shape,
D). Brushite crystals can also appear as plates with a granular surface. may be associated with AKI from ethylene glycol intoxication.

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48 SECTION II Investigation of Renal Disease

A B C

D E F

G H I
Figure 4-4 Crystals. A, Uric acid crystals. This rhomboid shape is the most common. B, Bihydrated calcium oxalate crystals with typical “letter envelope”
appearance. C, Different types of monohydrated calcium oxalate crystals. D, Star-like brushite (calcium phosphate) crystal. E, Struvite (triple phosphate)
crystal, on the background of a massive amount of amorphous phosphate particles. F, Cholesterol crystal. G, Cystine crystals heaped one on the other.
H, 2,8-Dihydroxyadenine crystal by bright-field microscopy; inset, by polarized light. I, Amoxicillin crystal resembling a branch of a broom bush.

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 CHAPTER 4 Urinalysis    49

J K
Figure 4-4, cont’d J, Star-like ciprofloxacin crystals as seen by polarized light. K, Large crystal of indinavir. (All images but 4-4.H and 4-4.J by phase
contrast microscopy; original magnification ×400.) (H courtesy Prof. Michel Daudon, Paris.)

Struvite crystals are often associated with urinary tract infection

caused by urea-splitting microorganisms such as Ureaplasma urea-
lyticum and Corynebacterium urealyticum.
Cholesterol crystals are found in association with other fatty
particles in patients with marked proteinuria. Again, cystine crystals
are a marker of cystinuria, and 2,8-dihydroxyadenine crystals
are associated with phosphoribosyltransferase enzyme deficiency.
Crystalluria resulting from drugs must be suspected whenever crys-
tals with unusual morphology are seen. In this setting, crystalluria
may be isolated and asymptomatic or associated with hematuria,
obstructive uropathy, or AKI caused by the precipitation of crystals
within the renal tubules.24

Organisms Figure 4-5 Egg of Schistosoma haematobium. Note the typical terminal
Bacteria are a frequent finding because urine is usually collected spike (arrow). (Phase contrast microscopy; original magnification ×400.)
and handled under nonsterile conditions and examination is often
delayed. Urine infection should be suspected only if bacteria are
found in noncontaminated, freshly voided midstream urine and INTERPRETATION OF URINE
especially if leukocytes are also present. Candida (yeasts), Tricho- SEDIMENT FINDINGS
monas vaginalis (protozoon), and Enterobius vermicularis (para-
site) are usually present as contaminants derived from genital Examination of the urine sediment, coupled with the quantity
secretions. of proteinuria and other urine and blood findings, results in urine
The parasite Schistosoma haematobium is responsible for urinary sediment profiles that aid in the diagnosis of urinary tract diseases
schistosomiasis (see Chapter 56). The examination of the urinary (Table 4-3).
sediment is the most widely used method for diagnosis of schistoso-
miasis, which causes microhematuria with recurrent bouts of mac-
rohematuria and obstructive uropathy. The diagnosis is based on the Nephrotic Syndrome
finding of the parasite eggs, with their typical terminal spike (Fig. The typical nephrotic sediment contains lipids, casts, and renal
4-5). The eggs are especially found between 10 AM and 2 PM and after tubular epithelial cell. Fatty, epithelial, granular, hyaline, and hyaline-
physical exercise, which favors the detachment of the eggs from the granular casts are seen, and erythrocyte or hemoglobin casts, leuko-
bladder mucosa. cyte casts, and waxy casts are absent or few. Erythrocytes may be
totally absent, especially in minimal change disease, or may be in low
Contaminants to moderate numbers (e.g., 3-5/hpf to 20-30/hpf), which is seen
A large number of particles can contaminate urine. These particles especially in membranous nephropathy and focal segmental glo-
may come from the patient (e.g., spermatozoa; erythrocytes from merulosclerosis. Leukocytes are usually not found.
menstruation; leukocytes from vaginitis, cloth or synthetic fibers,
creams or talcum), the laboratory (e.g., starch particles, glass frag-
ments from coverslips), or the environment (e.g., pollens, plant cells, Nephritic Syndrome
fungal spores).24 Correct identification of these particles is important Erythrocytes with erythrocyte and hemoglobin casts are the hall-
to avoid misinterpretation and false results (e.g., misdiagnosis of mark of the nephritic sediment. Usually, the number of erythrocytes
hematuria due to urine contamination from menstrual blood). ranges from 30 to 40 cells/hpf to more than 100 cells/hpf, with the

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50 SECTION II Investigation of Renal Disease

infection is caused by urease-producing bacteria, such as U. urealyti-

Main Urinary Sediment Profiles cum and C. urealyticum. In patients with renal infection, leukocyte
Renal Disease Hallmark Associated Findings casts and casts containing microorganisms may be found.
Nephrotic Fatty particles Renal tubular epithelial cells The correlation between the urine sediment findings and the
syndrome (RTECs) urine culture is usually good. False-positive results may be caused by
(proteinuria: RTEC casts urine contamination from genital secretions or bacterial overgrowth
++++) Erythrocytes (absent to on standing. False-negative results may be caused by the lysis of
moderate number)
leukocytes or misinterpretation of bacteria, especially with cocci.
Nephritic Erythrocytes Leukocytes (low number)
syndrome (moderate to RTECs (low number)
(proteinuria: high number) RTEC casts
+ → ++++) Erythrocyte/ Waxy casts BK Virus Infection
hemoglobin casts The serial examination of the urinary sediment, coupled with the
Acute tubular RTECs Variable according to cause
measurement of viremia, is useful to diagnose and monitor the reac-
necrosis (ATN; RTEC casts of ATN (e.g., myoglobin tivation of BK virus (BKV) in kidney transplant recipients,44 an event
proteinuria: Granular casts casts in rhabdomyolysis; which may lead to BKV nephropathy and graft loss (see Chapter
absent to uric acid crystals in acute 105). In BKV infection, the urine sediment contains variable numbers
trace) urate nephropathy;
of “decoy cells,” which are cells with nuclear changes caused by virus
erythrocytes in
proliferative/active invasion. The four decoy phenotypes identified45 are (1) nuclear
glomerulonephritis) ground-glass or gelatinous appearance; (2) intranuclear inclusion
Urinary tract Bacteria Isomorphic erythrocytes
surrounded by a clear halo (cytomegalovirus-like); (3) multinucle-
infection Leukocytes Superficial transitional ated cells; and (4) vesicular nuclei with clumped chromatin and
(proteinuria: epithelial cells nucleoli. In addition, cells with eccentric nucleus and comet-like
absent) Struvite crystals (for appearance are frequently seen in BKV infection, as well as hybrid
infections caused by
forms that represent transitions between the different phenotypes.
urease-producing bacteria)
Leukocyte casts (in renal Decoy cells are best identified by Papanicolaou stain performed
infection) on cytocentrifuged or smeared samples45 (Fig. 4-6, A). In our experi-
Urologic Isomorphic Transitional cells (deep, ence, decoy cells can easily be seen also by phase contrast microscopy
diseases erythrocytes (low superficial, atypical) in unstained samples46 (Fig. 4-6, B).
(proteinuria: to high number) The finding of decoy cells may indicate reactivation of BKV only
absent) Leukocytes or BKV nephropathy. Nephropathy is suspected when the number
Polyomavirus Decoy cells Decoy cell casts (in BK virus of decoy cells is high and persistent over time or casts containing
BK infection nephropathy) decoy cells are found, in the presence of BK viremia and renal dys-
(proteinuria: function.44,45,47 However, a definite diagnosis of BKV nephropathy
absent)
can be obtained only with renal biopsy.
Table 4-3 Main urinary sediment profiles.

higher figure found especially in patients with extracapillary or nec- Urologic Diseases
rotizing glomerular lesions. Leukocyturia is also common and is Urinary tract disorders such as cancer, urolithiasis, and hydrone-
mild (e.g., 3-5/hpf) in most patients, but in those with acute postin- phrosis are associated with the finding in the urine sediment of
fectious GN or active proliferative lupus nephritis, we have seen variable numbers of isomorphic erythrocytes, which are often asso-
samples with up to 30 to 40 leukocytes/hpf. Leukocyte casts and ciated with leukocytes or transitional epithelial cells (from deep or
waxy casts also may be observed. superficial layers of uroepithelium). In addition, in uroepithelial
The nephritic sediment may clear with treatment, but its reap- cancer, malignant transitional cells can be found, with abnormal size
pearance usually indicates relapse of the disease, such as lupus and shape, increased number and size of nuclei, and enlarged nucle-
nephritis42 or systemic vasculitis.43 Rarely, patients may have an oli. These cells can also be identified in unstained samples by phase
active proliferative GN without nephritic sediment. contrast microscopy.

Acute Tubular Necrosis Nonspecific Urinary Abnormalities

RTECs associated with epithelial casts and granular casts are the Some urine sediment findings are nonspecific. This occurs when
hallmark of the sediment of ATN but are not found in functional variable numbers of hyaline or hyaline-granular casts are found with
pre-renal AKI.33,36,37 In addition to RTECs, depending on the cause or without low numbers of erythrocytes, leukocytes, common crys-
of the tubular damage, other elements can be seen. These include tals, or small numbers of superficial transitional epithelial cells. In
myoglobin-pigmented casts in rhabdomyolysis, uric acid crystals such patients, especially if the findings persist over time, the correct
(usually in massive amounts) in acute uric acid nephropathy, and interpretation of the urinary findings requires adequate clinical
erythrocytes (high numbers) and erythrocyte casts in active prolif- information and the knowledge of other laboratory tests.
erative glomerular diseases.

AUTOMATED ANALYSIS
Urinary Tract Infection OF URINE SEDIMENT
Bacteria and leukocytes are the hallmarks of urinary tract infection,
in association with superficial transitional epithelial cells and iso- Instruments for the automated analysis of the urinary sediment are
morphic erythrocytes. Struvite crystals can also be present when the based on flow cytometry or digital imaging. Flow cytometry uses

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 CHAPTER 4 Urinalysis    51

A B
Figure 4-6 Decoy cells resulting from polyomavirus BK infection. A, Decoy cell with coarse, clumped chromatin, as seen by Papanicolaou stain.
B, Decoy cells with the nuclear ground-glass phenotype as seen by phase contrast microscopy. Inset, Decoy cell with comet-like appearance. (Original mag-
nification: A, ×1000; B, ×400.)

stains for nucleic acid and cell membranes in uncentrifuged urine 5. Bridgen ML, Edgell D, McPherson M, et al. High incidence of significant
samples to identify cells, bacteria, and casts.48 Accuracy is good for urinary ascorbic acid concentration in a West Coast population: Implication
for routine analysis. Clin Chem. 1992;38:426-431.
leukocytes and erythrocytes, even though the erythrocytes can be 6. Lam MO. False hematuria due to bacteriuria. Arch Pathol. 1995;119:
overestimated because of the interference from bacteria, crystals, and 717-721.
yeasts. False-negative results for casts are common, ranging from 7. Lamb EJ, MacKenzie F, Stevens PE. How should proteinuria be detected and
about 13% to 43%. measured? Ann Clin Biochem. 2009;46:205-217.
8. Guy M, Newall R, Borzomato J, et al. Use of a first-line urine protein-
Digital imaging systems supply quantitative results and black-
to-creatinine ratio strip test on random urines to rule out proteinuria in
and-white images of urine particles, which can be used to review patients with chronic kidney disease. Nephrol Dial Transplant. 2009;24:
the results. Currently, two main instruments are based on this tech- 1189-1193.
nology. The first shows the particles identified on the screen by 9. McIntyre NJ, Taal MW. How to measure proteinuria? Curr Opin Nephrol
categories (e.g., all epithelial squamous cells, all crystals), with a Hypertens. 2008;17:600-603.
10. Antunes VVH, Veronese FJV, Morales JV. Diagnostic accuracy of the protein/
good precision and accuracy for erythrocytes and leukocytes but creatinine ratio in urine samples to estimate 24-h proteinuria in patients with
rather low sensitivity for casts.49 The other instrument supplies primary glomerulopathies: a longitudinal study. Nephrol Dial Transplant.
whole-field images, similar to those obtained by bright-field manual 2008;23:2242-2246.
microscopy, and has good sensitivity for casts and epithelial cells as 11. Caring for Australians with Renal Impairment (CARI). The CARI guidelines.
Urine protein as diagnostic test: Performance characteristics of tests used in
well.50
the initial evaluation of patients at risk of renal disease. Nephrology. 2004;
Automated instruments are now used in large laboratories to 9:S8-S14.
screen large numbers of samples in a short time and to identify the 12. Price CP, Newall R, Boyd JC. Use of protein/creatinine ratio measurements
samples that are normal or that contain only minor changes. This on random urine samples for prediction of significant proteinuria: A system-
approach greatly reduces the number of samples that require manual atic review. Clin Chem. 2005;51:1577-1586.
13. Birmingham DJ, Rovin BH, Shidham G, et al. Spot urine protein/creatinine
microscopy. As yet, however, these instruments do not recognize a ratios are unreliable estimates of 24 h proteinuria in most systemic lupus
number of particles of clinical importance, such as lipids, cellular erythematosus nephritis flares. Kidney Int. 2007;72:865-870.
casts, deep epithelial transitional cells, RTECs, and various types of 14. Hebert LA, Birmingham DJ, Shidham G, et al. Random spot urine/protein/
crystals. Therefore, for the proper evaluation of the renal patient, creatinine ratio is unreliable for estimating 24-hour proteinuria in individual
systemic lupus erythematosus nephritis patients. Nephron Clin Pract. 2009;
manual microscopy with phase contrast and polarized-light devices
113:c177-c182.
is still the recommended approach. 15. Atkins RC, Briganti EM, Zimmet PZ, et al. Association between albuminuria
and proteinuria in the general population: The AusDiab Study. Nephrol Dial
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