Examination of The Urine Sediment: Specimen Collection

23
Examination of the Urine Sediment

Heather L. Wamsley
SPECIMEN COLLECTION usually produces a sample with the best morphology for cytological
Urinalysis results are influenced by the biological variability of patients, examination. However, seeding carcinoma cells in the abdominal wall
the urine collection method, the timing of urine collection, the admin- is an uncommon, but grave, complication of cystotomy and percuta-
istration of therapeutic or diagnostic agents before collection, and neous FNB.4
the method of handling the sample before analysis.1 Ideally, at least 6
milliliters (mL) of urine should be collected before the administration
SPECIMEN HANDLING BEFORE URINALYSIS
of therapeutic or diagnostic agents to establish baseline information;
however, in patients with cystitis and urge incontinence, this may be With proper sample handling and testing, complete urinalysis may
challenging. In urinalysis, 5 mL of urine may be used; 1 mL may be rapidly provide information about the genitourinary tract and screen
used for urine culture, if necessary. When choosing the urine collec- for diseases of other body systems (e.g., endocrine, hepatic). Urine
tion method and the timing of urine collection, it is useful to consider should be collected into a sterile, single-use vessel to avoid potential
the patient’s clinical status, the logistics of the collection method, and contamination by cleanser residues and microorganisms. The body of
the intended use of the sample (Tables 23.1 and 23.2). the container, not just the lid, should be labeled, and the container
First-morning, preprandial urine samples, which are inherently should be sealed to avoid leakage of the sample and evaporation of vol-
collected after a period of nil per os (NPO, nothing by mouth), will atile compounds (e.g., ketones). Urine specimen cups often leak during
have the highest urine specific gravity and the highest concentration of transport. If urine will be sent to a reference laboratory, it should be
sediment; however, the cytomorphology of the sediment contents and transferred to a labeled, plain, white-top tube. To minimize postcollec-
the viability of fastidious microorganisms may be reduced because of tion artifacts and to obtain results that are most representative of urine
the relatively prolonged retention of urine within the bladder. If sedi- in vivo, urine samples should be evaluated within 30 minutes of col-
ment examination and urine culture are primary goals, cystocentesis of lection.5 If urinalysis will be delayed, the sample should be refrigerated
a randomly timed urine sample may be preferred in patients without and protected from light to prevent overgrowth of microorganisms
contraindications for cystocentesis (e.g., thrombocytopenia, urethral and photodegradation of bilirubin, respectively. If necessary, sam-
obstruction). Cystocentesis samples are also useful to localize urinaly- ples may be stored for approximately 12 to 24 hours (i.e., overnight).
sis findings (e.g., sediment abnormalities, proteinuria) to the bladder However, depending on the initial sample composition (e.g., pH and
or proximal urinary tract because samples obtained via cystocentesis concentration of crystallogenic substances), the sediment content may
will lack contributions from the lower genitourinary tract. be modified from what was initially present immediately ex vivo—
Samples collected during midstream micturition or by transure- crystals may form with refrigerated storage (i.e., struvite, calcium oxa-
thral catheterization are also suitable for sediment examination and late dihydrate), renal tubular casts may degrade, and cytomorphology
quantitative urine culture, which should be interpreted by using may be detrimentally altered.6 Freezing or routine use of chemical
guidelines based on collection method and colony-forming units per preservatives should be avoided. Refrigeration is preferred for preser-
milliliter (CFU/mL) (Table 23.3). Manual compression of the bladder vation of urine samples. Because cold urine may influence urinalysis
to induce micturition should be avoided because doing so may cause results (e.g., falsely increase specific gravity, inhibit enzymatic urine
reflux of potentially infectious urine, traumatic hematuria, or, rarely, dipstick reactions, and promote crystal formation), a sample that has
uroabdomen. Voided urine samples rescued from the examination been refrigerated should be permitted to warm to room temperature
room tabletop have limited utility; but, if the sediment is examined before urinalysis. If crystalluria is a medically important problem that
without delay, some components can still be assessed, specifically cells is being diagnosed or monitored, then the finding should be confirmed
that might come from the patient (e.g., leukocytes, erythrocytes, atypi- in a freshly obtained sample collected into a single-use container and
cal cells). Such a sample should not be used for biochemical analysis or analyzed within 30 to 60 minutes without interim refrigeration.5,6
to screen for infectious organisms.
In addition to routine urine sediment evaluation, urine samples
PREPARATION OF URINE SEDIMENT WET MOUNT
may be converted to a dry-mount cytology sample2,3; this allows for
more sensitive detection of bacteria and more accurate assessment of Evaluation of the urine sediment for the presence of increased
bacterial morphology and greatly facilitates evaluation of atypical cells concentrations of cells, casts, microorganisms, or crystals is use-
in-house or by a reference laboratory. The method is described in Box ful for the detection of underlying urinary tract disease or diseases
23.1. If available, cytocentrifugation of the urine sediment is equally of other organs. Gross clarity of the urine sample should not be
useful. When possible, obtaining cells directly from a mass (i.e., ultra- used as the sole means to determine potentially normal sediment
sound-guided fine-needle biopsy [FNB] or surgical biopsy imprint) findings because even nonturbid samples may be abnormal on
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Examination of the Urine Sediment

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