Metabolic syndrome is a cluster of risk factors of metabolic origin; it is a construct designed to identify individuals at increased cardiovascular risk.

There are several definitions (including those from the World Health Organization and National Cholesterol Education Program's Adult Treatment Panel III); in each definition, the diagnosis is based on defining values for dyslipidemia, hypertension, impaired glucose tolerance, and obesity, with insulin resistance generally considered to be the common link.

The NCEP Adult Treatment Panel III defined metabolic syndrome as the occurrence of three or more of the following criteria (see diagnostic decision for details of further definitions):

• Abdominal obesity [waist circumference: >40 inches (>102cm) in men, >35 inches (>88cm) in women]
• Elevated levels of triglycerides [fasting blood triglycerides equal to or >150mg/dL (>1.7mmol/L)]
• Low levels of high-density lipoprotein (HDL) cholesterol <40mg/dL (<1.0mmol/L) for men, <50mg/dL (<1.3mmol/L) for women
• Elevated blood pressure (equal to or >130/85mmHg or documented use of antihypertensive therapy)
• Evidence of insulin resistance (fasting glucose equal to or >110mg/dL (>6.1mmol/L)). Although, the American Heart Association (AHA) in 2004 suggested glucose equal to or >100mg/dL (>5.5mmol/L) as an alternative cut-off point

Individually, the metabolic disorders are risk factors for cardiovascular disease, particularly coronary heart disease; some evidence suggests that metabolic syndrome increases cardiovascular risk beyond that expected from the individual risk factors alone, but this assertion has not been confirmed.

The metabolic syndrome label may be most useful as a reminder to physicians (and patients) that the presence of one element should heighten awareness that other elements are also likely to be present.

There has been recent concern that metabolic syndrome is imprecisely defined and less valuable as a cardiovascular risk marker than was originally thought. Consequently, some experts and organizations are recommending an emphasis on individual cardiovascular risk factors, regardless of whether or not criteria for metabolic syndrome are met.