Insulin Fasting(F Insulin)

A fasting insulin under 5 mIU/L typically reflects healthy insulin sensitivity in lean, metabolically intact adults. Values from 5 to 10 mIU/L sit in a borderline zone where dietary pattern, body composition, and training load all matter. Persistently elevated fasting insulin above 10 to 12 mIU/L in the presence of normal fasting glucose is the classical signature of compensated insulin resistance, where the pancreas is working harder to maintain euglycemia. The HOMA-IR index (fasting glucose multiplied by fasting insulin, divided by 405 for US units) integrates both numbers into a single insulin sensitivity score. HOMA-IR under 1.0 is generally considered insulin-sensitive; values above 2.5 to 3.0 indicate clinically meaningful resistance. The triglyceride-to-HDL ratio adds a third independent signal that often agrees with HOMA-IR. Insulin resistance precedes nearly every chronic disease of metabolic origin: type 2 diabetes, non-alcoholic fatty liver disease, cardiovascular disease, certain cancers, polycystic ovary syndrome, and increasingly Alzheimer's disease (sometimes called type 3 diabetes in the research literature). Crucially, fasting insulin is not on most standard chemistry panels in the US; patients usually have to request it specifically.