Definition and Diagnostic Criteria for Diabetes Mellitus and Other Categories of Glucose Intolerance

The term diabetes mellitus describes a metabolic disorder of multiple aetiology characterized by chronic hyperglycaemia with disturbances of carbohydrate, fat and protein metabolism resulting from defects in insulin secretion, insulin action, or both. The effects of diabetes mellitus include long–term damage, dysfunction and failure of various organs. Diabetes mellitus may present with characteristic symptoms such as thirst, polyuria, blurring of vision, and weight loss.

The requirements for diagnostic confirmation for a person presenting with severe symptoms and gross hyperglycaemia differ from those for the asymptomatic person with blood glucose values found to be just above the diagnostic cut–off value.

The diagnosis of diabetes in an asymptomatic subject should never be made on the basis of a single abnormal blood glucose value. For the asymptomatic person, at least one additional plasma/blood glucose test result with a value in the diabetic range is essential, either fasting, from a random (casual) sample, or from the oral glucose tolerance test (OGTT).

It may be appropriate to screen pregnant women belonging to high–risk populations during the first trimester of pregnancy in order to detect previously undiagnosed diabetes mellitus (Gestational diabetes).

Performance of the Oral Glucose Tolerance Test (OGTT)

1. After the person has fasted overnight (8-12 hours), a zero time (baseline) sample of blood is drawn.
2. The patient is given a standard dose of 75 g of glucose. The standard dose for an adult can be delivered as one bottle of GLUCODYN solution (or 75 g glucose dissolved in 200-300 millilitres of water). For children the dose is 1.75 g per kg of body weight. Total children’s dose should not exceed 75 g. Blood samples are taken at specific intervals to measure blood glucose and sometimes also insulin levels. The intervals and number of samples vary according to the purpose of the test. For simple diabetes screening, the most important sample is the 2-hour sample.
3. During the days preceding the glucose test, the patient should have eaten a diet high in carbohydrates. Bed patients should not be subjected to a glucose test because they often respond pathologically (resting in bed tends to impair the sugar tolerance).
4. Blood sample.
5. Serum should be separated from the cells within 30 min after the blood is drawn. Serum samples can be stored 2- 3 days in the refrigerator or they can be frozen. Whole blood samples can be analyzed too, but serum or plasma is recommended.
6. Measurement of glucose concentration.
7. The glucose concentration can be analyzed e.g. with hexokinase or glucose dehydrogenase method.

WHO Criteria (1999) for Interpreting 2 Hour Glucose Tolerance Test

Serum or plasma samples (fS-Gluk or fP-Gluk).

Normal glucose tolerance

• 0 h sample < 6.1 mmol/l
• 2 h sample < 7.8 mmol/l

Impaired fasting glucose (IFG)

• 0 h sample ≥ 6.1 mmol/l and < 7 mmol/l
• 2 h sample < 7.8 mmol/l

Impaired glucose tolerance (IGT)

• 0 h sample < 7.0 mmol/l
• 2 h sample ≥ 7.8 mmol/l and < 11.1 mmol/l

Diabetes mellitus (DM)

• 0 h sample ≥ 7.0 mmol/l
• 2 h sample ≥ 11.1 mmol/l

Results in whole blood glucose samples (fB-Gluk) are about 1 mmol/l lower than in serum or plasma samples.