The earliest detectable signal of insulin resistance — moves before glucose, often before HbA1c.
Fasting insulin is the earliest lab marker to flag developing insulin resistance — often elevated for years before fasting glucose creeps up and decades before HbA1c crosses the prediabetic threshold. A non-diabetic, "healthy" person can have fasting insulin of 15+ mIU/L and be metabolically unhealthy despite normal glucose.
The HOMA-IR calculation (fasting insulin × fasting glucose / 405) gives a quantified insulin sensitivity index. HOMA-IR >2.5 is insulin resistant; <1.5 is sensitive; <1.0 is excellent.
Fasting insulin is influenced by: insulin sensitivity (the dominant variable), recent carbohydrate load (must fast 12+ hours), body fat (especially visceral), exercise (lowers reliably), sleep quality (poor sleep raises), and pharmacologic agents — metformin lowers; berberine lowers; GLP-1s lower significantly; SGLT2is lower; corticosteroids raise; growth hormone peptides and HGH can raise modestly.
Pull alongside fasting glucose at baseline and 3 months on any metabolic intervention (GLP-1, metformin, dietary change). On GLP-1s expect 30–60% reductions at maintenance dose. On GH protocols (especially MK-677), watch for upward drift signaling insulin sensitivity decline. Pair with fasting glucose to compute HOMA-IR for the cleanest insulin sensitivity read.
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Start tracking →Informational only — not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.