Chapter LABORATORY DIAGNOSIS

41 OF DIABETES MELLITUS
2.. ^ fasting plasma glucose concentration >126 mgdi
The dagnosIs of diabetes isestablished by any one of the
on morc than onc occasion.
fout cntcna (American Diabctes AssOCiation 2014):
3. Abnormal oralglucose tolerance test (0GTT). in which
1. Arandom plasma glucose coneentration >200 mg/dl, the plasma glucose concentration is >200 mg/dl at 2
with classIcal sipns and symptoms of hypcrglyccmia hours after a standard carbohydrate load.
or hyperlycacmic crisis. 4. HbAlc>6.5%.

Table 41.1: Differences Between type 1and type 2 Diabetes Mellitus

PARAMETER TYPE 1DM TYPE 2 DM

Porcentago of allDM cases 5-10% 90-95%

Clinical foatures
a. Age of onset Childhood/adolescents Adults
b. Obesity Absent (weight loss) Common
c. Presentation Acute with classical symptoms Insidious
Insulin lovels Progressive decrease Early increase, later moderate decrease
Serum C peptido levels Very low to absent Normal to high
Circulating islet cell-antibodies anti-insulin, anti-GAD, anti-1CA512 Absent
Genetic predisposition Low Strong
Common acute complication Ketoacidosis Hyperosmolar hyperglycemic state

Table 41.2: Features oft Dlabetlc ketoacldosls and Hyperosmolar Hyperglycemic ^tate
Diabetic Ketoacidosis(DKA) Hyperosmolar Hyperglycemic
State(HHS)
Type of DM commonly affected Type 1 Type 2
Plasma Glucose (mg/dl) 250-600 mg/dl 600-1200 mg/dl
Sodium, meq/L 125-135 135-145
Osmolality (mOsm/ml) 300-320 330-380
Plasma/urine ketones +/
Arterial pH 6.8-7.3 (acidosis) >7.3 (no acidosis)
Arterial PCO,, mmHg 20-30 Normal
Anion gap [Na - (Ci + HCO)] increased Normal to slightly increased

GESTATIONAL DIABETES MELLITUS (GDM)

Onset or lirst recognitionof glucose intolerance during pregnancy is referred to as gestationaldiabetes mellitus.
Illeflects: High birth weight,cardiac defects, polyhydramnios, intrauterine fetal loSs, premature birth, pre-eclampsia.
Diagnosis: Onestep approach for high risk wonen (only oral glucose tolerance test/0GTT) and two step approach
for average risk wonen (sereening test followed by OGTT).
Outcome: Can return tonormal or have inpaired glucose tolerance or develop frank DM.
182
 183
Laboratory Diagnosis of Diabetes Mellitus
METABOLIC SYNDROME TESTS FOR DIAGNOSIS OF DM
Also known as insulin
resistance syndronne,
Reaven's syndrone or syndrome 1. Blood glucose
X.
Detined by three or more of the following live " Plasma is preferrcdas whole blood glucoseis affected
abnormalitics: waist cireumference > 102 cm in by conccntration of protcins espccially hemoglobins.
menor> 88 cm in women, serunn triglyceride levcl " Mcthods uscd: carlicr chcmical mcthods like Folin
of at least 150 mg/dl, HDL level of< Wu method, Somagyi-Nelson method, orthotoludine
40mg/dl in
men or << S0mg/dl in women, blood method were uscd, nowadays enzymatic methods like
lcast 130/85 mm lHg, and fasting pressurcofat glucose oxidase method, hexokinase method are used.
level > 10 mg/dl but <126 mg/dl. plasma glucosc Sample collection: In container with sodium fluoride
These paticnts have increased risk of developing which inhibits crythrocyte glycolysis.
diabetes mellitus.
2. Oral glucose tolerance test (0GTT)
PREDIABETES OR IMPAIRED GLUCOSE TOL Glucose tolerancemeans ability of the body to utilize glu
ERANCE (IGT) OR IMPAIRED FASTING GLU cose in blood circulation; it is decreased in diabetes melli
COSE (IFG) tus, hyperthyroidism, hyperpituitarism and hypoadrenalism.
It is a state where plasma glucose is higher than Normally blood sugar levels temporary rise after food in
normal but not high enough for diagnosis of take, and return to normal within two to three hours.
diabetes mellitus. Patient preparation: Carbohydrate rich unrestricted
It is referred to as impaired fasting glucose (IFG) diet for 2-3 days prior to test, fasting for 12-16 hours.
or impaired glucose tolerance (IGT) depending on No medication on the day of the test.
which test is used for its detection. " Method: Following steps are followed:
Majority of individuals develop type 2 DM within (A) Fasting venous blood sample is collected
ten years. (B) Give 75gm glucose to patient, dissolved
Prediabetic individuals have an increased risk of in water, lemon juice may be added.
cardiovascular disease. (C) A single venous sample is collected two
Development of DM can be prevented by weight hours after glucose load.
loss, diet modification and excercise. (D) Plasma glucose is estimated in fasting and
Interpretation of the OGTT in IGT is shown in two hour venous sample.
table 41.3 Interpretation of OGTT is shown in Table 41.3
Renal threshold refers to the amount of glucose in blood
LABORATORY TESTS IN DIABETES MELLITUS above which glucose appears in urine. Normal value is
around 180 mg/dl.
1. Laboratory tests for diagnosis of DM " Lowered renal threshold/renal glycosuria:
" Plasma glucose (fasting/post prandial/random). Threshold may be as low as 130-150 mg/dl, this
Oral glucose tolerance test (OGTT). is observed due to some abnormality in the tubular
2. Laboratory tests for screening of DM. absorption of glucose. Glucose appears in urine
Fasting blood glucose. even with normal plasma glucose.
3. Laboratory tests for glycemic control. Raised renal threshold: Threshold raised up to 250
Glycosylated hemoglobin (HbAlc). 300 mg/dl, this occurs with increasing age as a
result of atherosclerosis and in patients with
" Self monitoring of blood glucose.
prolonged diabetes mellitus.
4. Laboratory tests for long term complications of DM.
" Urinary albumin excretion. TESTS FOR GLYCEMIC CONTROL
" Lipid profile test.
1. Glycosylated hemoglobin (HbA1c)
5. Laboratory tests for acute complications of DM.
" Blood and urine glucose. " Refers to hemoglobin to which glucose is attached,
Blood and urine ketones. non enzymatically and irreversibly. It depends on
blood glucose level and lifespan of red cells.
Arterial pH/blood gas analysis. " It reflects the average blood glucose level for an ex
" Serum electrolytes. tended time period and it remains unaffected by the
Blood osmolality. short term fluctuations in blood glucose.
" Blood urea and serum creatinine. " Nornal levels 4 to 6%.
6. Laboratory tests for type I DM " Metlhod of measurement ion exchange method,
" Islet cell antibodies HPLC, chromatography or agar gel electrophoresis.
184 Essentials of Practical Pathology

Importance: Monioring with lbAle helps in im 2. Lipid profile test

poved glycacmia control whiech is associated with . T'ype Idiabctcs is associatcd with only a slight el
prevention and delaying diabetic complications. cvation of LDL cholcstcrol and serum triglycerides
" Advantages of using HbAlcare that there is no nced andlittle ifany change in HDL cholesterol. Once the
to fast for the test and it has lower intra individual hyperglyccmia is corrected, Iipoprotein levels are
gcncrally normal.
variability.
. In paticnts with type 2 diabetes, a distinct "diabetic
2. SELF MONITORING OF BLOOD GLUCOSE dyslipidemia" is characteristic of the insulin resis
" Capillary blood glucose mcasurement by glucomctcrs
tance syndrome. Its features are a high serum trig
done by patients thcmselves, arc cxtremcly useful. lyceride level (300-400mg/dl), a low HDL choles
" They should not be used for diagnosis as they lack
terol (< 30 mg/dl), and qualitative changes in LDL
particles. An annual lipid profile is indicated in all
precision. adult diabetes.
There are several paper strip (glucose Oxidase, glu
cose dehydrogenase, or hexokinase) methods for mea TEST FOR ACUTE COMPLICATIONS OF DM
suring glucose on capillary blood samples. A reflec
tance photometer or an amperometric system is then
used to measure the reaction that takes place on the 1. Urinary glucose
reagent strip. Urinary glucose correlates well with plasma glucose
These glucometers are accurate, but they vary with values. When the glucose value exceeds 180 mg/dl
regard to speed, convenience, size of blood samples i.e. renal threshold, glucose appears in urine.
required, reporting capability, and cost. Commonly used methods for urine glucose measurement
-Benedict's semiquantitative test, glucose strip test
TEST FOR LONG TERM COMPLICATIONS
2. Blood and urine ketones
1.Urinary proteins
" Ketone bodies are formed from metabolism of free
Persistent proteinuria detectable by routine screen fatty acids and include acetoacetic acid, acetone and
ing test (i.e. > 150 mg/24 hours) in a diabetic sug beta hydroxyl butyric acid.
gests diabetic nephropathy with irreversible damage. " Increased ketones in diabetics denote impending or
Method used for measurement of 24 hour urine pro established diabetic ketoacidosis, which is a medical
tein - Esbach's albuminometer.
emergency.
Increased urinary albumin excretion (less than 150 " Method used - colorimetric reaction with nitroprus
mg/24 hours) known as microalbuminuria, has been side (in both blood and urine).
observed in very early stage of diabetes when GFR is
normal and permanent renaldamage has not occurred. Reference values
Hence it is used as marker of subsequent develop
ment of proteinuria and diabetic nephropathy. Plasma glucose <100mg/dl(fasting)
" Method used for measurement of microalbuminuria < 140 mgldl (postprandial)
Reagent strip tests are available, positive results Glycosylated hemoglobin
should be confirmed by semi quantitative tests e.g. (HbA1c) 4-6 %

enzyme immunoassay or radio immunoassay. Total cholesterol <200mg/dlI

Serum triglyceride levels <150 mg/dl
To diagnosis microalbuminuria, at least two out of >60 mg/dl
High density lipoprotein (HDL)
three different samples should test positive over a
period of3-6 months. Lowdensity lipoprotein (LDL) <130 mg/dl

Table 41.3: Interpretation of oral glucose tolerance test (0GTT)

Normal DM IGT/Prediabetes

Fasting plasma glucose <100mg/dl >126 mg/dl 100-125 mg/dl

2h OGTT <140 mg/dl >200 mgldl 140-199 mg/dl
HbA1c <5.7% >6.5% 5.7-6.4%