Fasting insulin
Also reported as: Serum insulin
How much insulin the pancreas is secreting to hold fasting glucose where it is.
Wide, and essentially uninformative — most laboratory upper bounds sit deep in the insulin-resistant range.
Metabolic-medicine convention. Insulin-sensitive adults typically sit between 2 and 6 µIU/mL; above about 10 suggests meaningful compensation is underway.
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Where the thresholds sit
| Band | Range (µIU/mL) | Note |
|---|---|---|
| Optimal | 2–6 | — |
| Acceptable | 6–10 | — |
| Early resistance | 10–15 | — |
| Resistant | > 15 | — |
Why it matters
The earliest routinely available signal of insulin resistance, and the one most often left off a standard panel. Insulin rises for years to compensate before glucose or HbA1c budge, so a normal glucose with a high insulin is a warning that a glucose-only panel misses entirely.
What raises it
- Insulin resistance and visceral adiposity
- Chronic carbohydrate excess
- Sleep deprivation
- Physical inactivity, within days
- Polycystic ovary syndrome
What lowers it
- Resistance training
- Weight loss
- Carbohydrate restriction
- Improved sleep
- Metformin
How to move it
- 1Resistance training two or three times a week. Skeletal muscle disposes of most post-meal glucose, and more of it means less insulin needed.
- 2Get sleep above seven hours — insulin sensitivity is measurably worse after even a few short nights.
- 3Reduce visceral fat specifically. Waist circumference tracks this better than weight.
- 4Walk after meals.
- 5Retest at 12 weeks; this marker responds faster than HbA1c.
What moves this marker
Interventions on this site with evidence behind them for this specific marker. None of them replaces working out why yours is where it is.
What makes a single reading misleading
- Assay methods differ between laboratories, so compare results from the same lab where possible.
- Must be genuinely fasted — even a small amount of food invalidates it.
- Not useful in type 1 diabetes or in anyone on exogenous insulin.
Sources
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Educational only. Reference ranges are not diagnostic thresholds and this page cannot account for your medical history, medication or symptoms. Discuss any result that concerns you with a qualified clinician. See our medical disclaimer.