Diagnostic Tests for Diabetic Blood Sugar Levels
Diagnostic tests are conducted for screening purposes to diagnose
diabetes, and ongoing laboratory tests are conducted to evaluate the
effectiveness of diabetic management. Definitions of diabetic blood sugar
levels vary in clinical practice, depending on the laboratory that performs
the tests, but nearly all agree that glucose levels within certain ranges
constitute a diagnosis of diabetes.
Three diagnostic tests may be used to diagnose diabetes, and each must be
confirmed, on a subsequent day, with one of the three tests. The diagnostic
criteria for diabetic blood sugar levels as recommended by the American
Diabetes Association are:
1. Symptoms of diabetes plus casual plasma glucose concentration greater
than 200 mg/dL. Casual is defined as any time of day without regard to time
since the last meal.
2. Fasting plasma glucose greater than 126 mg/dL. Fasting is defined as no
caloric intake for eight hours.
3. Two hour plasma glucose greater than 200 mg/dL during an oral glucose
tolerance test. The test should be performed with a glucose load containing
the equivalent of 75 anhydrous glucose dissolved in water.
When using these criteria, the following levels are used for fasting plasma
glucose.
• Normal fasting glucose = 110 mg/dL.
• Impaired fasting glucose = to or greater than 110 and less than 126 mg/dL.
• Diagnosis of diabetes = to or greater than 126 mg/dL.
When using these criteria, the following levels are used for the oral
glucose tolerance test.
• Normal glucose tolerance = 2 hour plasma glucose: less than 140 mg/dL.
• Impaired glucose tolerance = 2 hour plasma glucose: greater than 140 mg/dL
and less than 200 mg/dL.
• Diagnosis of diabetes = 2 hour plasma glucose: greater than 200 mg/dL.
Note that although either method may be used to diagnose diabetes, in a
clinical setting the fasting blood glucose is the recommended screening test
for diabetic blood sugar levels in non-pregnant adults.
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