Insulin resistance: how it is measured

The thing everyone talks about and nobody measures directly

Insulin resistance is the state where your tissues respond less to insulin, so the pancreas makes more of it to get the same effect. For years before blood sugar rises at all, insulin can be climbing to hold it down. That is why someone can have a normal glucose and still be well down a metabolic road.

Measuring it properly is another matter.

The gold standard, and why you will never have it

The hyperinsulinaemic‑euglycaemic clamp is the reference method. Insulin is infused at a fixed rate while glucose is infused at whatever rate keeps blood sugar steady; how much glucose it takes tells you how well insulin is working. It takes hours, needs two lines and constant monitoring, and exists in research units.

Every other method is an approximation of it, and should be read as one.

HOMA-IR, the usual compromise

HOMA‑IR is calculated from a fasting glucose and a fasting insulin drawn at the same moment. The arithmetic differs by units — with glucose in mg/dL it is glucose × insulin ÷ 405; in mmol/L it is glucose × insulin ÷ 22.5.

Its weaknesses are worth knowing before you pay for it:

• Insulin assays are not standardised. Different laboratories using different platforms can return meaningfully different insulin values on the same sample, and HOMA‑IR inherits that.
• There is no agreed cut‑off. Published thresholds vary by population and by study. A number without the laboratory's own reference range attached means very little.
• It describes the fasting state only, which is not where most insulin resistance shows itself first.

It is still useful, particularly repeated in the same laboratory over time, where the direction of travel matters more than the absolute figure.

The cheap proxies

Two things already on an ordinary panel carry information about insulin resistance and cost nothing extra:

• Triglyceride to HDL ratio. Both come from the lipid panel. A high ratio is associated with insulin resistance in several populations, though the thresholds that have been proposed differ between ethnic groups and the evidence is weaker in some than others.
• Waist circumference. Unfashionable, free, and a better predictor of metabolic trouble than weight or BMI. Measured at the midpoint between the lowest rib and the top of the hip bone, at the end of a normal breath out.

Neither is a measurement of insulin resistance. Both are signals that it is likely, which is usually what a clinician actually needs.

Why our baseline does not include fasting insulin

Fasting insulin is an immunoassay and costs around ₡18,000 — more than twice a fasting glucose. We left it out of the baseline deliberately, and the question that settled it was: would the result change what we do next?

For most people arriving with fatigue and stalled weight, it would not. Glucose, HbA1c, triglycerides and HDL between them already say whether the metabolic picture is worrying, and the next step is the same either way.

Where it does change a decision — a normal HbA1c with a strong family history, or a picture that does not add up — it goes on as an addition. That is what the per‑treatment list is for.

What none of this measures

Insulin resistance is not one thing. The liver, muscle and fat can be resistant to different degrees in the same person, and no blood test on this page separates them. Published thresholds also come largely from European and North American cohorts, and how well they transfer to a Costa Rican population is not something we can answer from the literature we have read.

What it means for you depends on the rest of your results and your history, which is a conversation with a physician rather than a calculation.