What are the diagnostic criteria for diabetes mellitus ?
The American Diabetic Association and medical authorities recently revised the standards for diabetes mellitus and a "borderline" condition known as Impaired Glucose Tolerance (IGT). Three values are generally measured in diabetics.The fasting blood sugar is a value determined after not eating or drinking anything but water for approximately 8-12 hours prior to testing. A normal value is less that 116 mg%. People with IGT have values <126 mg% but above 115 mg%, while individuals with fasting glucose values above 126 mg% confirmed with a second separate sample meet the criteria for diabetes mellitus.
The 2-hour glucose is measured 2 hours after drinking a glucose solution given as part of a glucose tolerance test. This test is not usually required to make the diagnosis of diabetes. A "casual" or "random" blood glucose is measured without a pre-test fast. Values over 200 mg% meet a criterion for diabetes mellitus. Blood sugar levels between 140-200 mg% represent IGT, while normal individuals will have levels below 140 mg%.
Impaired Fasting Glucose (IFG) is a condition that is a risk factor for later development of diabetes. People with fasting levels between 110 and 126 mg% have IFG.
A third value commonly measured is the glycosylated haemoglobin or haemoglobin A1C. This test is not a direct increase of blood sugar but gives a picture of the general range of glucose over the previous 3-4 months. A normal individual will have less than 7% of their haemoglobin with glucose molecules attached. Diabetics tend to have 7% or more of their haemoglobin with glucose molecules attached. Hgb A1C values vary significantly from laboratory to laboratory. Changes in Hgb A1C occur slowly over weeks to months and are only useful in trend analysis of diabetes management. The diagnosis of diabetes is not made by Hgb A1C levels, but elevated levels are suggestive of the diagnosis. Newer tests, such as serum frucosamine, may be more useful as a short term glucose trend analysis and a management tool.
