Insulin (Fasting / Random)
Insulin is made by pancreatic beta cells and released in response to rising blood glucose. It drives glucose into cells for energy and suppresses liver glucose production. Fasting insulin, combined with fasting glucose, is used to calculate HOMA-IR — a measure of insulin resistance. Insulin testing is not routine for diagnosing diabetes (glucose and HbA1c are preferred) but helps evaluate PCOS, reactive hypoglycemia, and suspected insulinoma.
Reference Ranges
Male
3 – 25
µIU/mL
Female
3 – 25
µIU/mL
Child
Consult pediatrician
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Fasting insulin below 3 µIU/mL with normal or low glucose is usually normal and seen in lean individuals. In a known diabetic, very low insulin with high glucose suggests type 1 diabetes (insulin deficiency) and a need for insulin replacement.
What High Levels Mean
Fasting insulin above 25 µIU/mL indicates insulin resistance — the pancreas is producing extra insulin to overcome tissue resistance. Very high insulin with low glucose suggests insulinoma (rare) or sulfonylurea use. Most commonly, high fasting insulin reflects metabolic syndrome, PCOS, obesity, or early type 2 diabetes.
Frequently Asked Questions
Do I need to fast for an insulin test?
For a meaningful result, yes — 8–12 hours of fasting. Fasting insulin is what feeds into HOMA-IR and reflects basal insulin resistance. Random insulin values depend entirely on what and when you last ate and are rarely useful without a paired glucose measurement from the same draw.
Should insulin be tested for diagnosing diabetes?
No. Fasting glucose, HbA1c, and oral glucose tolerance are the standard diagnostic tests for diabetes. Insulin adds useful information in specific situations — PCOS, suspected insulin resistance in lean patients, reactive hypoglycemia — but is not a replacement for glucose-based tests.
What does high insulin with normal glucose mean?
This pattern describes compensated insulin resistance — the pancreas is still keeping glucose in range, but it is working harder to do so. It is an early warning sign for type 2 diabetes and metabolic syndrome. Lifestyle changes (weight loss, exercise, reduced refined carbs) at this stage can often reverse the pattern before diabetes develops.
Related Hormones tests
See all →HOMA-IR (Insulin Resistance Index)
Calculated index that estimates insulin resistance.
indexHormonesBeta-hCG (Human Chorionic Gonadotropin)
Pregnancy hormone — also a tumor marker for certain cancers.
mIU/mLHormonesSex Hormone Binding Globulin (SHBG)
Protein that binds sex hormones in blood, controlling their availability.
nmol/LHormonesTotal Testosterone
Total blood level of the main male sex hormone.
ng/dLThis information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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