The World Health Organization (WHO) and many other organizations around the world such as National Diabetes Data Group of United States have issued diagnostic criteria for diabetes mellitus based on certain facts such as (1) the spectrum of fasting plasma glucose (FPG) and the response to an oral glucose load (OGTT or oral glucose tolerance test) varies among different normal individuals, and (2) diabetes mellitus should be diagnosed if the level of blood glucose is at or higher, at which diabetes-specific complications occur.

For example the criteria for diagnosis of diabetes mellitus given below may not be applicable to Native Americans (Pima Indian population) because the prevalence of retinopathy (a complication of diabetes) begins to increase at fasting plasma glucose of more than 6.4 mmol/Liter (116 mg/100 ml of blood).

The following is Criteria for the Diagnosis of Diabetes Mellitus:

• Fasting (no caloric intake for at least 8 hours) plasma glucose of more than or equal to 7.0 mmol/Liter (126 mg/100 ml of blood) or
• Symptoms of diabetes plus random (without regard to time since the last meal) blood glucose concentration of more than or equal to 11.1 mmol/Liter (200 mg/100 ml of blood) or
• Two-hour plasma glucose of more than or equal to 11.1 mmol/Liter (200 mg/100 ml of blood) during an oral glucose tolerance test (done with a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water). This is not recommended for routine use.

If any of the above criteria is positive conclusively than diagnosis of diabetes mellitus should be done. In the absence of unequivocal hyperglycemia and serious metabolic disorder, these criteria should be confirmed by repeat testing on a different day to diagnose diabetes mellitus.

Glucose tolerance is of three types (1) Fasting plasma glucose of less than 5.6 mmol/Liter (100 mgs/100 ml of blood) is normal glucose tolerance (2) Fasting plasma glucose of 5.6–6.9 mmol/Liter (100–125 mg/100 ml of blood) is defined as IFG or Impaired Fasting Glucose (3) Fasting plasma glucose of more than or equal to 7.0 mmol/Liter (126 mg/100 ml of blood) is diabetes. Based on the OGTT (oral glucose tolerance test), IGT is plasma glucose level of 7.8 to 11.1 mmol/Liter (140 and 199 mg/100 ml of blood) and diabetes is defined as a glucose more than 11.1 mmol/Liter (200 mg/100 ml of blood) 2 hours after a 75-gram oral glucose load. The American Diabetes Association (ADA), recently designated individuals with IFG and/or IGT, as pre-diabetes and they are at much higher risk of developing type-2 diabetes (25%–40% risk over the next 5 years) and also have an increased risk of cardiovascular disease.

The current criteria for diagnosis of diabetes gives more emphasis to fasting plasma glucose (FPG) as it is the most reliable and convenient, especially for identifying diabetes in asymptomatic individuals. A random plasma glucose concentration of more than or equal to 11.1 mmol/Liter (200 mg/100 ml) along with classic symptoms namely polyuria, polydipsia, weight loss is also sufficient for the diagnosis of diabetes mellitus.

The diagnosis of diabetes mellitus has profound implications for an individual from both a medically as well as financially, hence the diagnostic criteria should be fulfilled satisfactorily before diagnosing diabetes. In case of any doubt as may be found after screening, the tests should be repeated to confirm diagnosis.

NB: Some authors advocate the estimation of glycosylated hemoglobin (A1C) for diagnosis of diabetes mellitus, as there is a strong correlation between elevations in the plasma glucose and the A1C. But it is not recommended for routine diagnosis of diabetes as relationship between the fasting plasma glucose and the A1C in individuals with mild glucose intolerance is less clear.

The revised criteria for diagnosis of diabetes mellitus also allow the withdrawal of diagnosis of diabetes if the fasting plasma glucose reverts to normal.

Source:

The American Diabetes Association (ADA), 2007.