In 1997, the ADA issued new diagnostic and classification criteria; in 2003, modifications were made regarding the diagnosis of impaired fasting glucose (IFG). The classification of diabetes includes four clinical classes:
* Type 1 diabetes (results from ??-cell destruction, usually leading to absolute insulin deficiency).
* Type 2 diabetes (results from a progressive insulin secretory defect on the background of insulin resistance).
* Other specific types of diabetes due to other causes, e.g., genetic defects in ??-cell function, genetic defects in insulin action, diseases of the exocrine pancreas (such as cystic fibrosis), and drug or chemical induced (such as in the treatment of AIDS or after organ transplantation).
* Gestational diabetes mellitus (GDM) (diagnosed during pregnancy).
* The FPG is the preferred test to diagnose diabetes in children and nonpregnant adults. (E)
* The use of the A1C for the diagnosis of diabetes is not recommended at this time. (E)
Criteria for the diagnosis of diabetes in nonpregnant adults are shown in Table 2. Three ways to diagnose diabetes are available, and each must be confirmed on a subsequent day unless unequivocal symptoms of hyperglycemia are present. Although the 75-g oral glucose tolerance test (OGTT) is more sensitive and modestly more specific than fasting plasma glucose (FPG) to diagnose diabetes, it is poorly reproducible and rarely performed in practice. Because of ease of use, acceptability to patients, and lower cost, the FPG is the preferred diagnostic test. It should be noted that the vast majority of people who meet diagnostic criteria for diabetes by OGTT, but not by FPG, will have an A1C value <7.0%. The use of the A1C for the diagnosis of diabetes is not recommended at this time.
Table 2??a glucose 200 mg/dl (11.1 mmol/l) during an OGTT. The test should be performed as described by the World Health Organization, using a glucose load containing the equivalent of 75-g anhydrous glucose dissolved in water.
Hyperglycemia not sufficient to meet the diagnostic criteria for diabetes is categorized as either IFG or impaired glucose tolerance (IGT), depending on whether it is identified through a FPG or an OGTT:
* IFG = FPG 100 mg/dl (5.6 mmol/l) to 125 mg/dl (6.9 mmol/l)
* IGT = 2-h plasma glucose 140 mg/dl (7.8 mmol/l) to 199 mg/dl (11.0 mmol/l)
Recently, IFG and IGT have been officially termed “pre-diabetes.” Both categories, IFG and IGT, are risk factors for future diabetes and cardiovascular disease (CVD).
In the absence of unequivocal hyperglycemia, these criteria should be confirmed by repeat testing on a different day. The OGTT is not recommended for routine clinical use but may be required in the evaluation of patients with IFG (see text) or when diabetes is still suspected despite a normal FPG, as with the postpartum evaluation of women with GDM.
AMERICAN DIABETES ASSOCIATION
DIABETES CARE, VOLUME 27, SUPPLEMENT 1, JANUARY 2004
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