A High Fasting Insulin with a Normal Glucose
A normal glucose can be bought at very different prices. If your pancreas is producing two or three times as much insulin as someone else's to hold the same number, the glucose result tells you the compensation is working and nothing about how hard it is working. Fasting insulin measures the price.
The pattern on your report
- Fasting insulin High · moderate Key
- Fasting glucose Normal Key
- HbA1c Normal Key
- Triglycerides High-normal Supporting
Printed as: Fasting glucose in mmol/Lor mg/dLHbA1c in mmol/molor %— Not a simple multiplication: (mmol/mol divided by 10.929) plus 2.15.Fasting insulin in pmol/Lor mIU/L— Genuinely different figures: 60 pmol/L is about 10 mIU/L. Assays are poorly standardized, so a value from one laboratory should not be judged against another's range.Triglycerides in mmol/Lor mg/dL
Why the numbers look like this
Insulin's job includes telling the liver to stop releasing glucose overnight and telling muscle and fat to take it up. When tissue responds poorly, the pancreas compensates by secreting more, and the extra output keeps glucose in range.
That compensation can continue for many years, which is why glucose is a late marker. Insulin rises first, glucose follows only when the beta cells can no longer keep up, and by then a meaningful share of their capacity is gone.
HOMA-IR is the arithmetic that combines the two, multiplying fasting insulin by fasting glucose and dividing by a constant. It is a rough index rather than a measurement, but it captures the idea the pair is expressing: how much insulin it is costing to hold that glucose.
Not being flagged is not the same as normal
Fasting insulin assays are poorly standardized between laboratories, which is the main limitation of this test and the reason it is not part of routine practice in most places. The printed range is also a population reference from people who mostly already have some degree of insulin resistance, so being inside it is weak reassurance. That combination means the number is more useful for tracking a direction over time in one laboratory than for comparing against a threshold.
What else on the report can hide this
The physical signs are more reliable than the assay and cost nothing. Waist circumference is the most useful measurement here. Skin tags and velvety dark patches at the neck, armpits or groin are visible markers of insulin resistance and frequently precede any laboratory abnormality.
The rest of the panel converges. Triglycerides up with HDL down is the lipid signature, a mildly raised ALT points at fat in the liver, urate drifts up because insulin reduces its excretion, and blood pressure follows.
In women, irregular periods, acne or excess hair growth alongside this pattern raise polycystic ovary syndrome, where insulin resistance is central and the fasting insulin explains symptoms that get treated separately.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
Insulin resistance from central adiposity
The dominant cause. Waist circumference matters more than weight, and visceral fat drives it more than subcutaneous.
- Very common
Physical inactivity
Muscle takes up glucose independently of insulin during and after exercise, so losing activity raises insulin requirement directly.
- Common
Metabolic fat in the liver
Both a consequence and a driver. A mildly raised ALT alongside, and the liver's own resistance raises fasting insulin specifically.
- Common
Polycystic ovary syndrome — in women of reproductive age
Insulin resistance is central to it. Irregular periods, acne or excess hair growth, and it is often diagnosed years after the metabolic changes began.
- Common
Medications
Steroids, some antipsychotics and certain antiretrovirals raise insulin resistance substantially.
- Common
Poor or insufficient sleep
Even short periods of restricted sleep measurably reduce insulin sensitivity, and sleep apnea does so persistently.
- Common
Assay variation between laboratories
Insulin assays are not well standardized, so a single value from one laboratory should not be compared against a threshold from elsewhere.
- Rare
An insulinoma
A tumor secreting insulin autonomously, producing symptomatic low glucose rather than normal glucose. The glucose direction is what excludes it here.
What is usually checked next
- Waist circumference More informative than the assay, more reproducible, and available in any consulting room.
- HOMA-IR calculated from fasting insulin and glucose Combines the pair into a single index, useful for tracking direction in one laboratory over time.
- Lipids, ALT, urate and blood pressure Shows whether the full cluster is present, which is more convincing than the insulin alone.
- Oral glucose tolerance test Reveals post-meal rises that fasting numbers miss, and shows how the compensation performs under load.
- A sleep and activity history Two major modifiable contributors, neither of which appears on any blood test.
When to seek care sooner
- Same day Heavy thirst, passing large volumes of urine, or unexplained weight loss
- Soon Episodes of shakiness, sweating or confusion relieved by eating
- Soon Velvety dark patches of skin at the neck or armpits appearing quickly
- Soon Irregular or absent periods with excess hair growth
- Soon An HbA1c or fasting glucose that has now crossed a threshold
Questions worth bringing to your appointment
- What is my waist measurement, and where does it sit?
- Has HOMA-IR been calculated from these two numbers?
- Do my lipids, ALT and blood pressure fit the same picture?
- Given my symptoms, is polycystic ovary syndrome worth considering?
- What changes the direction at this stage?