Normal Fasting Insulin Level: Range Chart & What's Optimal

Standard metabolic panels focus on fasting glucose and HbA1c — markers that become abnormal late in the disease process. Fasting insulin isn't part of routine screening guidelines because the clinical establishment focuses on diagnosing diabetes, not preventing it. Functional and integrative practitioners include it because it detects dysfunction 10-15 years earlier.

You can request it from your doctor (CPT code 83525), order it through our comprehensive panel, or use a direct-to-consumer lab service. The test requires a 12-hour overnight fast. Blood should ideally be drawn before 10 AM. For a closer look at at-home collection kits and other direct-to-consumer options, see our insulin resistance testing guide.

Optimal fasting insulin is below 5 μIU/mL, which indicates excellent insulin sensitivity. A level of 5–7 μIU/mL is good with low risk. Above 7–10 μIU/mL indicates early insulin resistance — years before fasting glucose rises abnormally. Most standard labs report 'normal' as up to 24.9 μIU/mL, meaning a level of 18 μIU/mL would come back 'normal' on your report despite indicating significant insulin resistance. This gap between 'normal' and 'optimal' is why functional medicine practitioners treat fasting insulin as one of the most important early metabolic markers.

With consistent dietary intervention — primarily reducing refined carbohydrates and added sugars, increasing fiber and protein, and reducing total caloric load — fasting insulin typically begins improving within 2–4 weeks and shows measurable reductions (20–40%) within 8–12 weeks. Resistance training improves insulin sensitivity acutely within 24–48 hours of a single session and cumulatively over weeks. Significant reductions of 30–50% in fasting insulin are achievable in 12 weeks with diet and exercise combined. People who also add time-restricted eating or intermittent fasting often see faster early improvements.

No — they're two separate results from the same blood draw, measuring two different things. Fasting glucose measures the sugar circulating in your blood; fasting insulin measures the hormone your pancreas released to keep that sugar in range. You can have a completely normal fasting glucose (under 100 mg/dL) while your fasting insulin is already elevated, because the pancreas compensates by producing more insulin long before glucose control breaks down — this is exactly why fasting insulin catches metabolic dysfunction earlier than glucose alone. The two numbers are usually ordered together specifically so they can be combined into the HOMA-IR index described above, or run through our insulin resistance calculator. For how fasting insulin stacks up against a third common marker, see our fasting insulin vs. A1C comparison.

Coverage depends on why it's ordered. When a doctor requests fasting insulin (CPT code 83525) to work up a documented complaint — weight changes, PCOS, a strong family history of diabetes — most U.S. insurance plans and Medicare process it like other diagnostic bloodwork, though a copay or deductible may still apply. Because fasting insulin isn't part of most standard insurance-covered diabetes screening panels, plans are more likely to decline coverage when it's ordered purely for proactive screening without a supporting diagnosis code. Without insurance, cash-pay pricing for a standalone fasting insulin test is typically well under $150 through direct-to-consumer lab services, though exact pricing varies by lab, region, and whether a physician-order fee is bundled in. Confirming coverage with your insurer, or asking about self-pay pricing upfront, avoids a surprise bill.

The reference ranges above don't change by sex — the same cutoffs apply to men and women — but insulin resistance is dramatically more common in women with polycystic ovary syndrome (PCOS). A peer-reviewed NIH-published review notes that most women with PCOS are metabolically resistant to insulin, whether from genetic propensity or excess weight, and it can be present even at a normal body weight (see our insulin resistance at a normal weight guide). Because insulin resistance drives much of the excess androgen production behind PCOS symptoms — irregular cycles, acne, hair thinning — fasting insulin (or HOMA-IR) is one of the most useful labs for a woman investigating possible PCOS, even when fasting glucose and A1C still look normal. If PCOS is suspected, pair this result with the full picture in our PCOS overview.

μIU/mL and mIU/L are the same unit under different names — you can compare those results to the table above with no conversion needed. Converting to pmol/L is trickier than most online calculators suggest: many tools use a factor of ×6.945, but immunoassay-standardization research has found that factor overstates the conversion. A 2019 analysis in the Journal of Diabetes Science and Technology found the widely-used ×6.945 factor is disputed against the standardized factor most assay bodies now favor. Because different labs calibrate against different insulin standards, the safest approach isn't to convert a pmol/L result yourself — it's to compare it against the reference range your own lab prints on the report.

Yes, but a very low fasting insulin is far less often a concern than a high one — and the number only means something when read together with your fasting glucose, not on its own. A single low result (roughly under 2–3 μIU/mL) is usually explained by something benign around the blood draw: an extended fast or notable caloric restriction in the day or two before testing, a very low-carbohydrate or ketogenic diet that trains the body to run on less circulating insulin, or genuinely high insulin sensitivity in someone lean and active. None of those, by themselves, is a red flag — they simply mean the pancreas needs to release less insulin to keep blood sugar steady. The differential that does warrant attention is reduced insulin production from the pancreas itself, as seen in early Type 1 diabetes or latent autoimmune diabetes in adults (LADA), where the immune system gradually damages the insulin-producing beta cells. The distinguishing feature is glucose: beta-cell failure shows up as low insulin paired with a normal-to-high fasting glucose, because too little insulin is being made to keep blood sugar in range — not low insulin alongside a normal or low glucose, which is the pattern in the benign causes above. A low fasting insulin with a normal fasting glucose is not, by itself, a reason for alarm. If a low result appears alongside an elevated fasting glucose (100 mg/dL or higher) or symptoms like unexplained weight loss, excessive thirst, or frequent urination, that combination is worth discussing with a doctor promptly, since together they can point toward a beta-cell problem rather than typical insulin resistance.

No — a high fasting insulin level on its own is not a diabetes diagnosis. Diabetes is diagnosed using fasting glucose, HbA1c, or an oral glucose tolerance test; fasting insulin isn't part of the standard diagnostic criteria at all, which is also why it isn't part of routine screening (see the FAQ above on why standard bloodwork skips it). What an elevated fasting insulin shows instead is that the pancreas is working harder than normal to keep blood sugar in the normal range — the compensatory hyperinsulinemia described above, and often the earliest detectable sign of the process that can progress toward prediabetes and eventually type 2 diabetes if left unaddressed. A high fasting insulin with a normal fasting glucose and A1C generally means you're catching a metabolic problem years before it would show up on standard diabetes screening, not that you already have the disease. An isolated elevated reading is still worth discussing with a doctor, and is best interpreted alongside fasting glucose and A1C — or the HOMA-IR calculation above — rather than the insulin number in isolation.