In 1997, the American Diabetes Association Expert Committee on the Diagnosis and Classification of Diabetes Mellitus established a new classification system and diagnostic criteria to define various states of abnormal glucose metabolism
(43). Fasting plasma glucose was divided into three diagnostic categories: (1)
normal < 110 mg/dL (6.1 mmol/L); (2) impaired fasting glucose (IFG) 110 to
125 mg/dL (6.1 to 6.9 mmol/L); and (3) diabetes mellitus > 126 mg/dL (7.0 -o mmol/L). Likewise, the plasma glucose 2 h after a 75-g oral glucose load (OGTT) |
was used to define three diagnostic categories: (1) normal glucose tolerance <
140 mg/dL (7.8 mmol/L); (2) impaired glucose tolerance 140 to 199 mg/dL (7.8 t to 11.1 mmol/L); and (3) diabetes mellitus > 200 mg/dL (11.1 mmol/L). Diabe- 5
tes can also be diagnosed by a casual plasma glucose > 200 mg/dL (11.1 mmol/ Ja
L) in conjunction with classic symptoms of diabetes, including polyuria, polydip- J
sia, and unexplained weight loss. To establish a diagnosis of diabetes using either a
& u the fasting or 2-h OGTT plasma glucose criteria, the result must be confirmed by repeat testing on another day.
The rationale used for establishing these diagnostic categories is that several studies have demonstrated a close, although not perfect, association between a fasting plasma glucose concentration of 126 mg/dL and the 2-h OGTT value of 200 mg/dL and both of these levels correlate well with the appearance of microvascular complications of diabetes including retinopathy, nephropathy, and neuropathy. It is also recognized that IFG and IGT are both conditions that are associated with an increased risk of developing overt type 2 diabetes mellitus and an increased risk for cardiovascular disease. Although these criteria are based solely on measurements of plasma glucose, they do, in fact, reflect the interaction between insulin resistance and pancreatic beta-cell function as described previously. There is now great interest in examining the effects of lifestyle modifications that emphasize weight reduction and increased physical exercise or treatment with medications that decrease insulin resistance, enhance insulin secretion, or work through other mechanisms to prevent or delay progression from IGT to diabetes in high-risk individuals.
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