The Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) is a simple, validated index of insulin resistance derived from fasting plasma glucose and fasting insulin. Developed by Matthews et al. in 1985.

Formula: HOMA-IR = (FPG mg/dL × FI µIU/mL) / 405

Indian populations have lower cutoffs than Caucasian populations due to higher body fat percentage at lower BMI (thin-fat Indian phenotype).

• <1.0: Normal insulin sensitivity
• 1.0-2.0: Average
• 2.0-2.5: Borderline — lifestyle intervention
• >2.5: Insulin resistance (AIIMS / Singh 2013)
• >3.8: Severe — metabolic syndrome highly likely; full workup indicated

Western literature often uses >2.7 or >2.9. Asian-Indian cutoff is lower because of higher visceral adiposity at same BMI.

• PCOS workup — ~70% of Indian PCOS patients have IR; metformin indicated if HOMA-IR >2.5
• NAFLD — IR is the central driver; check before labelling cryptogenic
• Prediabetes with normal HbA1c and FPG — IR may be the only clue
• Acanthosis nigricans in children/adolescents
• Metabolic syndrome screen with central obesity

The same lab values give HOMA-β: HOMA-β = (360 × insulin) / (glucose − 63). Normal is ~100%. Falling HOMA-β indicates beta-cell exhaustion — usually starts 5-10 years before clinical diabetes in Indians. Trend HOMA-β annually in high-risk patients to time metformin initiation.

• Not reliable on insulin therapy (gives confused readings)
• Inaccurate in advanced beta-cell failure (HbA1c >9%)
• Inter-lab variability for insulin assays — use the same lab for serial tests
• Single time-point — affected by stress, illness, recent steroids
• Pregnancy — physiological IR is normal; do not use HOMA-IR (use OGTT)