The diagnostic criteria for DM have been modified in recent years by the American Diabetes Association (ADA) from previous recommendations made by the National Diabetes Data Group in 1979 and the World Health Organization (WHO) in 1985. In clinical practice, establishing the diagnosis of diabetes is seldom a problem. When symptoms of hyperglycemia exist (thirst, polyuria, weight loss, etc.) a random plasma glucose concentration of > 11.1 mmol/l (200 mg/dl) or a fasting plasma glucose (FPG) of > 7.0 mmol/l (126 mg/dl) confirms the diagnosis. Where diagnostic difficulty exists, the precise diagnosis can be established with an oral glucose tolerance test (OGTT) using a 75 g anhydrous glucose load dissolved in water: a 2 h value > 11.1 mmol/l (200 mg/dl) establishes the diagnosis of diabetes. A confirmatory test using one or other of the three methods should be employed. The OGTT is not recommended for routine clinical use, but may be an important test for epidemiologic purposes where using the FPG only may lead to lower prevalence rates than with the combined use of the FPG and OGTT. The ADA recognizes an intermediate group of subjects whose FPG is > 6.1 mmol/l (110mg/dl) but <7.0mmol/l (126mg/dl) and has defined this group as having impaired fasting glucose (IFG). It has recently been suggested by the ADA that the FPG level to diagnose IFG should be reduced from >6.1 mmol/l (110mg/dl) to >5.6mmol/l (100mg/dl). A further abnormal category is defined as having a plasma glucose > 7.8 mmol/l (140mg/dl) but <11.1 mmol/l (200mg/dl) at 2h when an OGTT is used and is described as impaired glucose tolerance (IGT).
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