Fasting insulinHOMA-IR
How much insulin your body needs at rest to keep blood sugar in check.
Fasting insulin is the amount of insulin circulating after roughly eight hours without food. It is measured far less often than fasting glucose and it frequently changes first, which is the case for knowing what it is.
The logic is straightforward. Insulin resistance means cells respond less readily, so the pancreas produces more to achieve the same effect. For years that compensation succeeds, holding glucose in the normal range while insulin quietly climbs. Measuring only glucose therefore misses the early half of the process.
It is the input, with glucose, to HOMA-IR, the homeostasis model assessment published by Matthews and colleagues in 1985, which estimates insulin resistance from the two fasting values together. It is an estimate rather than a measurement, since the reference method is a clamp study nobody has done casually, but it is far better than either number alone.
Interpretation is genuinely unsettled, which is worth saying plainly. Laboratory reference ranges are wide, assays differ between labs so results are not directly comparable, and the optimal ranges quoted by private testing services are rarely derived from outcome data.
That makes it a useful trend and a poor single verdict. A high fasting insulin with normal glucose is a real signal worth acting on; a mildly raised value in isolation, from one lab, on one morning, is not a diagnosis of anything.
What moves it is the familiar list, and it moves reasonably quickly: losing visceral fat, regular aerobic and resistance training, building muscle as the main glucose sink, and sleep.
In practice, if you are investigating metabolic health properly, ask for fasting insulin alongside glucose and HbA1c rather than instead of them, and take the interpretation to a clinician.
Sources
Where your own result would sit
Most people reading this page are holding a blood-test report with this marker on it, and the question they arrived with is whether their number is normal. A reference interval says where most results from a healthy population fall; a guideline threshold is where a clinical body draws a line for a decision. Neither is a target, and a result on the wrong side of one is not a diagnosis: the same number can be unremarkable in one person and worth looking into in another, which is why the clinician who ordered the test reads it against your history rather than against a list.
Everyone
- Typical range
- under 12 mIU/L
- Above typical
- 12 mIU/L and over
FASTING SAMPLES ONLY; insulin rises steeply after eating. Converted from the source's 72 pmol/L using the standard factor of 6.0 pmol/L per mIU/L. Insulin assays are not standardised between platforms, so the same sample can read differently at different laboratories: treat this as a rough guide rather than a boundary. Reference intervals differ between laboratories and assays. Where your own report prints a range, the dashboard draws that one instead of this.
Reference interval from Oxford University Hospitals NHS Foundation Trust. Read against that page on 2026-08-09. Your own laboratory may print a slightly different range.
On your own blood test?
Fasting insulin is one of the markers FitTools can read from an uploaded blood-test report. You confirm every value before anything is saved, your own laboratory’s printed range is used in place of the one above wherever your report carries one, and your results are explained together in one place.