Fasting Insulin / HOMA-IR
Fasting insulin and glucose combined into a single index — fasting insulin × fasting glucose ÷ 22.5 — as an estimate of insulin resistance. The physiological rationale is sound: insulin resistance can precede dysglycaemia by years and independently associates with cardiometabolic risk.
Matthews DR, Hosker JP, Rudenski AS, et al. “Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man.” Diabetologia 1985;28(7):412–419 is the original validation against the euglycaemic clamp, and HOMA-IR does correlate with future type 2 diabetes and cardiometabolic risk in cohort studies. What it lacks is standardisation and consequence. Fasting insulin assays are not standardised across laboratories or platforms, reference ranges vary widely, no major guideline recommends routine HOMA-IR screening in asymptomatic adults, and no trial shows that acting on an isolated elevated HOMA-IR — beyond what glucose and HbA1c already prompt — changes outcomes.
Matthews DR, et al. Diabetologia. 1985. PubMed: PMID 3899825