Biomarker guide
Fasting Insulin (µIU/mL)
Fasting insulin measures how much insulin your pancreas is producing after an overnight fast. People test it because it can reveal how hard the body is working to keep glucose normal, insulin often rises years before fasting glucose or HbA1c drift out of range.
Reference ranges
Commonly used adult reference ranges. Labs vary in methodology and cutoffs, interpret your results against your lab report's stated ranges and with your doctor.
Commonly used reference ranges accept up to ~25 µIU/mL, but many clinicians view single-digit fasting insulin as the more informative target; assays vary by lab.
| Zone | Range |
|---|---|
| Low | 0–2 µIU/mL |
| Optimal | 2–10 µIU/mL |
| Above optimal | 10–25 µIU/mL |
| High | 25–30 µIU/mL |
The importance of Fasting Insulin
Insulin is the hormone that moves glucose out of the bloodstream and into cells. When cells become less responsive to it, the pancreas compensates by making more, so glucose can look perfectly normal while insulin quietly climbs. That is why fasting insulin is often described as an early-warning marker of insulin resistance.
A fasting insulin in the low single digits alongside normal glucose is generally associated with good insulin sensitivity. Higher values, especially when paired with rising triglycerides, a growing waistline, or creeping fasting glucose, paint a picture worth paying attention to. Some clinicians combine fasting insulin and glucose into a HOMA-IR score to estimate insulin resistance.
Because insulin assays are less standardized between labs than glucose assays, comparing results from the same lab over time is more meaningful than comparing across labs. A high or rising fasting insulin is worth discussing with your doctor, particularly alongside your glucose and lipid results.
Frequently asked questions
What is a normal fasting insulin level?
Commonly used lab reference ranges for fasting insulin run from roughly 2 to 25 µIU/mL, though many clinicians consider values under about 10 µIU/mL more consistent with good insulin sensitivity. Insulin assays differ between labs, so trends within one lab are the most reliable comparison.
Why test insulin if my glucose is normal?
Because insulin can rise years before glucose does. The pancreas often compensates for early insulin resistance by producing more insulin, holding glucose in the normal range while the underlying workload increases. Fasting insulin makes that hidden effort visible, which is why some people track it alongside glucose and HbA1c.
What is HOMA-IR?
HOMA-IR is a calculation that combines fasting insulin and fasting glucose into a single estimate of insulin resistance. It is computed as (glucose in mg/dL × insulin in µIU/mL) ÷ 405, with lower values associated with better insulin sensitivity. It is a screening estimate, not a diagnosis, and results are worth reviewing with your doctor.
What can raise fasting insulin?
Insulin resistance is the most common driver, but recent carbohydrate-heavy meals, inadequate fasting before the draw, stress, poor sleep, and certain medications can also elevate a reading. Repeating the test under consistent conditions helps separate a one-off result from a real trend.
Panels that measure Fasting Insulin
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