The metabolic syndrome — a cluster of cardiovascular risk factors — is defined by three of five criteria: waist circumference >40 inches (men) or >35 inches (women), triglycerides ≥150 mg/dL, HDL <40 mg/dL (men) or <50 mg/dL (women), blood pressure ≥130/85, or fasting glucose ≥100 mg/dL. Metabolic syndrome affects approximately 35% of US adults and dramatically increases risk of cardiovascular disease and Type 2 diabetes. It is often identified only when several criteria are present — but individual components deserve attention long before the full syndrome emerges.
Fasting insulin is one of the most clinically useful early metabolic markers — and one of the least ordered tests in standard care. In insulin resistance, insulin rises for years before fasting glucose elevates above the diabetic threshold. A patient with fasting glucose of 95 and fasting insulin of 20 µIU/mL has a very different metabolic trajectory than one with fasting glucose of 95 and fasting insulin of 5. HOMA-IR (fasting glucose × fasting insulin / 405) quantifies insulin resistance; a value above 2.0 signals early insulin resistance.
Triglycerides-to-HDL ratio is an inexpensive, underutilized cardiovascular risk marker. A ratio above 3.0 (in mg/dL units) strongly correlates with insulin resistance and small, dense LDL particle predominance — the most atherogenic LDL pattern — even when standard LDL appears normal. In patients with a high TG:HDL ratio, ApoB or LDL particle number provides a more accurate cardiovascular risk assessment than standard LDL.
Waist circumference (not BMI) is the most clinically relevant adiposity measure. Visceral fat — the metabolically active fat surrounding abdominal organs — drives insulin resistance, inflammation, and cardiovascular risk in ways that subcutaneous fat does not. BMI cannot distinguish between lean muscle mass and visceral fat and is a poor surrogate for metabolic risk in muscular individuals. Waist circumference above the thresholds above is a direct indication of visceral adiposity.