Diabetes Mellitus- Diagnostic Tests

DIAGNOSTIC TESTS

Diabetes may be present when sugar is present in the urine or when the blood sugar after fasting (12 hours after the last meal) or two hours after meals (post - prandial) is higher than 120 mg / 100 ml. Diagnosis of diabetes is confirmed after an oral glucose tolerance test.

Oral Glucose Tolerance Test (OGTT)

This test is carried out after 12 hours of over night fasting. Glucose

- 75g in adults and 1.75g/kg of body weight in children is orally administered. Before the glucose load and two hours after it, blood samples are collected and glucose levels are estimated.

The diagnostic criteria for diabetes and impaired glucose tolerance test (IGT) are given below. In normal persons without diabetes the fasting sugar levels vary between 80 - 110 mg / 100 ml. The blood sugar levels increase after the glucose load and come down to basal level within two hours.

List : Diagnostic Criteria for IGT and diabetes

Blood sugar levels (mg/dl)

Fasting   - IGT : < 120        Diabetes : >120

2 hours after 75g glucose load      - IGT : 120 - 180 Diabetes:     > 180

< stands for 'less than'

> stands for 'equal to more than'

Urinary Sugar

Glucose is excreted into the urine when the blood glucose levels are elevated beyond 180 mg / 100 ml. Diabetics lose varying amounts of glucose depending on the severity of disease and the dietary intake of carbohydrates. The approximate amount of urinary sugar can be easily monitored by the available diagnostic strips (uristix). The changes in the colour of the reagent or strip indicate sugar levels in the urine.

Benedict's Test

Eight drops of urine and 5 ml of Benedicts solution are taken in a test tube and mixed. The test tube is kept in boiling water for 5 minutes and colour is noted..

It is better to carry out this test on the second urine sample collected in the morning as urine sugar in this sample will more or less reflect blood sugar level.

Glycosylated hemoglobin - ( Hb A_1c )

As the concentration of glucose in blood rises, more glucose gets attached to hemoglobin (a pigment present in RBC) and the combined molecule is chemically estimated as glycosylated hemoglobin. It reflects the general trend of glucose levels in the blood during the previous 2 - 3 months. In normal individuals the glycosylated hemoglobin concentrations vary from 4 - 7% while in diabetics it is 8 - 18% of the total hemoglobin depending on the blood sugar level.