By the time HbA1c clears the prediabetes threshold, the underlying insulin resistance has often been building for years. Fasting insulin — drawn alongside fasting glucose — gives you an earlier view.

What fasting insulin measures

The amount of insulin circulating in your bloodstream after an overnight fast. When tissues become less responsive to insulin, the pancreas compensates by making more — so rising fasting insulin with still-normal glucose is an early signal of insulin resistance.

What the numbers mean

Reference ranges vary by lab and assay, typically running to around 25 μIU/mL as "normal." Many metabolic-health-focused clinicians aim for values well below that — often under 10, sometimes under 5 — for patients optimizing for long-term metabolic health. HOMA-IR, calculated from fasting insulin and fasting glucose, provides another way to read the pair together.

Why trend matters more than any single reading

Insulin is more variable than glucose, and a single draw can be skewed by recent meals, stress, or illness. Two or three values over a year paint a better picture than any one. Pairing fasting insulin with fasting glucose at every draw is more useful than either alone.

What can move it

Body fat (particularly visceral), carbohydrate intake, sleep deprivation, and physical inactivity tend to raise it. Weight loss, resistance training, cardiovascular exercise, and improved sleep tend to lower it. Several diabetes medications (metformin, GLP-1 agonists) also affect insulin dynamics.

How VisitRecall tracks it

Pair fasting insulin and glucose on the same timeline — and keep the whole metabolic picture in one place. See lab tracking and the longevity hub.

FAQ

Why don't standard physicals include it?

Most screening guidelines rely on glucose and A1C. Fasting insulin isn't routinely ordered unless someone asks for it or there's a specific indication.

How do I calculate HOMA-IR?

HOMA-IR = (fasting insulin μIU/mL × fasting glucose mg/dL) / 405. Many lab reports will calculate it automatically when both values are ordered.

Do I need to fast longer than for a lipid panel?

Typically 8–12 hours, water only. Follow your lab's instructions.