A fasting insulin of 21.5
21.5 µIU/mL
Within the lab range but raised
Fasting insulin of 21.5 µIU/mL is inside the printed reference range but above the level associated with good insulin sensitivity by commonly reported reference ranges
| Where it fallscommonly reported reference ranges | Within the lab range but raised |
|---|---|
| Fasting insulin | 21.5µIU/mL |
| Usual reference range | 2 – 25, though metabolic health is usually discussed below 10µIU/mL |
| HOMA-IR at a fasting glucose of 90insulin × glucose ÷ 405 — under about 2.0 is usually called insulin sensitive | 4.8 |
| Below the reference range | under 2µIU/mL |
| Within range, metabolically favourable | 2 – 10µIU/mL |
| Within the lab range but raisedthis reading | 10.1 – 24.9µIU/mL |
| Above the reference range | 25.1 and aboveµIU/mL |
Notes
- One reading is not a diagnosis. Fasting insulin moves with body fat, physical activity, sleep, and how long insulin resistance has been developing — often years before blood sugar moves. A clinician reads it against your history and usually against a repeat, not on its own.
- Reference ranges differ between laboratories. The bands above follow commonly reported reference ranges. Your own report prints the range its analyser was calibrated against, and that printed range is the one to compare against — a difference of a few units between labs is normal and does not mean either is wrong.
- Insulin rises years before blood sugar does. The pancreas compensates for growing resistance by producing more, and fasting glucose stays normal for as long as that compensation holds. Someone with a fasting insulin of 21.5 and a perfectly normal glucose can be well down that road — which is exactly why this test gets ordered when an A1C looks fine but the clinical picture does not.
- HOMA-IR here is 4.8. The index combines fasting insulin and fasting glucose; under about 2.0 is generally called insulin sensitive, and above roughly 2.9 is commonly used as a cut-off for resistance in research. The thresholds are not standardised across laboratories, and the index is a research tool that migrated into clinical use rather than the other way round.
- The reference range and the target are not the same thing. Most labs print an upper limit near 25 µIU/mL, derived from a population in which insulin resistance is common. Much of the literature on metabolic health discusses fasting insulin under 10, and some under 6. A result inside the printed range is not automatically a result you would choose.
- It must be fasting, and assays differ. Eight to twelve hours without food, and no comparing a value from one laboratory with a value from another — insulin assays are not standardised the way glucose is, and the same sample can return meaningfully different numbers.
What fasting insulin of 21.5 µIU/mL means
A result of 21.5 µIU/mL falls in Within the lab range but raised by commonly reported reference ranges.
The usual reference range is 2 – 25, though metabolic health is usually discussed below 10 µIU/mL.
Reading it next to the rest of the panel
Almost no blood test answers a question on its own. Each one narrows the field, and what narrows it further is the value sitting beside it on the same report — which is why a printout with one figure circled is harder to interpret than the whole page.
The bands here come from a named source rather than a rounded rule of thumb. A threshold is a decision point somebody argued for in print, and knowing which document a line comes from is what separates a meaningful result from a borderline one.
Nearby sizes
Read more
- CBC Normal Ranges — What Each Line on the Result MeansA value marked high or low on a CBC is common and is often not significant on its own. The pattern across lines is what a clinician reads.
- eGFR Normal Range: Above 90, and the Stages Below IteGFR is an estimate built from creatinine, age and sex — and the estimate is better than the raw creatinine it comes from, for a reason worth understanding.
- TSH Normal Range: 0.4–4.0 mIU/L, and the Number Moves BackwardsTSH runs opposite to the gland it measures. High TSH means the thyroid is underactive, and that inversion catches almost everyone reading their own result.
- Cholesterol Numbers: What Total, LDL, HDL and Triglycerides MeanA lipid panel reports four numbers and the one printed largest — total cholesterol — is the least useful of them.