Diabetic Screening Test

TESTS
The best screening test for diabetes, the fasting plasma glucose (FPG), is also a component of diagnostic testing. The FPG test and the 75-g oral glucose tolerance test (OGTT) are both suitable tests for diabetes; however, the FPG test is preferred in clinical settings because it is easier and faster to perform, more convenient and acceptable to patients, and less expensive. An FPG ≥126 mg/dl (7.0 mmol/l) is an indication for retesting, which should be repeated on a different day to confirm a diagnosis. If the FPG is <126 mg/dl (7.0 mmol/l) and there is a high suspicion for diabetes, an OGTT should be performed. A 2-h postload value in the OGTT ≥200 mg/dl (11.1 mmol/l) is a positive test for diabetes and should be confirmed on an alternate day. Table 2 presents the diagnostic criteria for diabetes. Fasting is defined as no consumption of food or beverage other than water for at least 8 h before testing.
Nondiabetic individuals with an FPG ≥110 mg/dl (6.1 mmol/l) but <126 mg/dl (7.0 mmol/l) are considered to have IFG, and those with 2-h values in the OGTT ≥140 mg/dl (7.8 mmol/l) but <200 mg/dl (11.1 mmol/l) are defined as having IGT. Both IFG and IGT are risk factors for future diabetes. Normoglycemia is defined as plasma glucose levels <110 mg/dl (6.1 mmol/l) in the FPG test and a 2-h postload value <140 mg/dl (7.8 mmol/l) in the OGTT.

If necessary, plasma glucose testing may be performed on individuals who have taken food or drink shortly before testing. Such tests are referred to as casual plasma glucose measurements and are given without regard to time of last meal. A casual plasma glucose level ≥200 mg/dl (11.1 mmol/l) with symptoms of diabetes is considered diagnostic of diabetes. A confirmatory FPG test or OGTT should be completed on a different day if the clinical condition of the patient permits.
Laboratory measurement of plasma glucose concentration is performed on venous samples with enzymatic assay techniques, and the above-mentioned values are based on the use of such methods. The A1C test values remain a valuable tool for monitoring glycemia, but it is not currently recommended for the screening or diagnosis of diabetes. Pencil and paper tests, such as the American Diabetes Association’s risk test, may be useful for educational purposes but do not perform well as stand-alone tests. Capillary blood glucose testing using a reflectance blood glucose meter has also been used but because of the imprecision of this method, it is better used for self-monitoring rather than as a screening tool.