Fasting Insulin
The level of insulin in the blood after fasting, an early marker of insulin resistance.
| Typical reference range | 2–19.6 uIU/mL |
| Commonly cited optimal range | 2–8 uIU/mL |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Insulin is made by beta cells in the pancreas and allows cells to take up glucose. In the fasting state, a small amount of insulin keeps the liver from releasing too much glucose.
Why it matters
When cells become resistant to insulin, the pancreas compensates by producing more, so fasting insulin often rises years before glucose or HbA1c become abnormal. It is used with glucose to calculate HOMA-IR.
What a high result can mean
High fasting insulin suggests insulin resistance, commonly linked to abdominal obesity, fatty liver, PCOS, inactivity and metabolic syndrome. It also rises if the sample is not truly fasting, with corticosteroids, and rarely with insulin-producing tumors.
What a low result can mean
Low insulin with high glucose suggests reduced insulin production, as in type 1 diabetes or advanced type 2 diabetes. Low insulin with normal glucose usually reflects good insulin sensitivity.
What affects the result
A strict 8-12 hour fast is essential; even a small snack raises insulin. Assays differ between labs and there is no universal standardization. Exercise, weight loss, sleep and reducing refined carbohydrates lower it. Biotin supplements can interfere with some immunoassays.
Units and conversion
Usually reported in uIU/mL.
- From pmol/L: multiply by 0.144 to get uIU/mL
- From mIU/L: multiply by 1 to get uIU/mL
- From mU/L: multiply by 1 to get uIU/mL
- From uU/mL: multiply by 1 to get uIU/mL
- From uIU/L: multiply by 0.001 to get uIU/mL
Also called on lab reports
Insulin, Insulin, Fasting, Insulin, Serum, Insulin (Fasting)
Related tests: Glucose & Metabolic
This page is educational and does not replace advice from a healthcare professional.