Definition of Metabolic Syndrome

There has been disagreement in the medical community over the definition of the metabolic syndrome. The National Heart, Lung, and Blood Institute collaborated with the American Heart Association to examine the issues associated with the definition. Their report is available online at http://www.circulationaha.org.

The metabolic syndrome seems to have three potential etiologies: obesity and disorders of adipose tissue; insulin resistance; and a constellation of independent factors (e.g., molecules of hepatic, vascular, and immunologic origin) that mediate specific components of the metabolic syndrome. Other factors such as aging, proinflammatory state, and hormonal changes also have been implicated.

The clinical criteria for the diagnosis of metabolic syndrome, as defined in the National Cholesterol Education Program’s Adult Treatment Panel III (ATP III) report, include waist circumference of more than 102 cm (40 in) in men and more than 88 cm (35 in) in women; triglyceride levels of at least 150 mg per dL (1.70 mmol per L); high-density lipoprotein cholesterol levels of less than 40 mg per dL (1.04 mmol per L) in men and less than 50 mg per dL (1.30 mmol per L) in women; blood pressure of at least 130/85 mm Hg; and fasting glucose levels of at least 110 mg per dL (6.10 mmol per L).

ATP III did not include impaired glucose tolerance, as detected by an oral glucose tolerance test (OGTT) or two-hour postglucose challenge, in the risk factors for metabolic syndrome. Its added value for determining cardiovascular risk appears small, and the benefit did not outweigh the inconvenience and cost of administering the OGTT in clinical practice. However, conference participants suggested adding OGTT at the physician's discretion in patients without diabetes with ATP III–defined metabolic syndrome or two or more metabolic risk factors. In the absence of impaired fasting glucose, impaired glucose tolerance could count as a risk factor to define metabolic syndrome.