Fasting Insulin and Early Detection

Why this comes up at all

Every standard annual panel measures your blood glucose. Almost none measure the hormone holding it there.

That is not an oversight. Standard panels are built to detect disease, and by that standard glucose is the diagnostic marker while insulin is not. It is a defensible design for its purpose.

It is also why insulin resistance routinely goes unmeasured for years while every annual result reads normal, and why a great many people are told their blood sugar is fine right up until it is not.

The sequence is worth stating plainly. Cells become less responsive to insulin. The pancreas compensates by producing more. More insulin does the job. Glucose comes back down. Everything reads normal.

That compensation can run for years, and during all of it a fasting glucose and an HbA1c are accurately reporting a system that is working. They are simply not reporting what it costs.

What the human evidence actually shows

The most useful recent work is not about insulin alone, it is about what combining tests reveals, which turns out to be the more actionable finding.

A 2026 systematic review and meta-analysis in BMJ Nutrition, Prevention and Health screened 11,980 papers from MEDLINE, Embase and Global Health, and included 40 original studies of adults with prediabetes published between 2006 and 2024. The aim was to determine which single or combination biochemical tests best predict progression to diabetes.

The meta-analysis found the highest risk of progression in the impaired fasting glucose group at 6.1 to 6.9 mmol/L, with a hazard ratio of 9.0.

More practically, descriptive statistics identified that the combination of impaired fasting glucose at 6.1 to 6.9, plus impaired glucose tolerance, plus an HbA1c of 6.0 to 6.4 percent had the highest annual incidence of diabetes, at 15.2 percent.

The authors stated it generally: combination tests were associated with higher progression rates than single tests, and certain combinations may allow better identification of who is likely to progress.

The review also noted there is no consensus on diagnostic criteria, with no single modality shown to be most predictive, which is an honest statement of where the field is.

On the surrogate side, a 2024 systematic review in Biomedicines covering 32 studies and 49,782 participants supported the triglyceride to HDL ratio as a simple and accessible marker of insulin resistance, reporting average cutoffs of about 2.53 for women and 2.8 for men, while noting predictive power varied by ethnicity and sex.

And a 2020 review in Canadian Family Physician worked through the limitations of HbA1c, which reads falsely low when red cell survival is shortened and falsely high in iron deficiency anaemia, among other conditions.

What this means in practice

The first consequence is about ordering, and it follows directly from the combination finding. If more doors open means more risk, then running one test tells you about one door.

Fasting insulin alongside HbA1c gives you the effort and the result together, from one draw. That is a materially different picture than either alone.

The second consequence is free, and most people can act on it tonight. Your triglyceride to HDL ratio is calculable from a lipid panel already sitting in your records, by dividing triglycerides by HDL in the same units. A ratio above roughly 2.5 to 2.8 is the flag suggesting the direct measurement is worth ordering.

The third is a caution about HbA1c specifically. Because it depends on red cells living a normal lifespan, an abnormal blood count or an iron problem distorts it. If your ferritin or blood count is off, read your HbA1c with that in mind rather than at face value.

The fourth is about timing your test. A 2021 randomized crossover study found four nights of four-hour sleep produced hyperinsulinaemia, hyperglycaemia and measurable insulin resistance in healthy young men. Test insulin during a stretch of bad sleep and you may measure your schedule.

And the fifth is the encouraging one. The progression rates in that review differ enormously between groups, which is precisely because trajectory responds to what people do.

The honest hedge

I am not a doctor and I am not diagnosing anyone, and diabetes is a diagnosis that requires one.

On fasting insulin reference ranges I want to be straight about where the ground is soft. Most labs report roughly 2 to 25 microIU/mL, which is wide enough to include a great deal of insulin resistance. Practitioners working functionally generally aim below about 5 to 7, and that target comes from consensus and physiological reasoning rather than from outcome trials establishing a cutoff.

So the right use of this test is to find out whether compensation is running, and to track your own trend, rather than to chase an exact number that the literature has not settled.

The 2026 review said the same thing about the field more broadly: no consensus on diagnostic criteria, no single modality shown to be most predictive. That is an honest description rather than a weakness in the argument for measuring.

I would also not want the framing to become alarming. Insulin resistance found early is the good version of this result, because it is the version where diet, resistance training, walking after meals and sleep still have years to work.

And a value in the diabetes range is a medical finding needing a doctor promptly rather than a lifestyle project.

What to do with this

Tonight, calculate your triglyceride to HDL ratio. Divide the two from a lipid panel you already have, using the same units. Free, and it tells you whether ordering more is worthwhile.

Order the pairing rather than a single test. Fasting insulin with HbA1c, from one draw. The combination finding is the practical takeaway from the progression research.

Fast properly for the insulin. At least eight hours with water, morning draw. Insulin responds within minutes to food, so a non-fasting result is uninterpretable.

Sort your sleep before testing if it is broken. Four nights of short sleep measurably changed these markers in healthy young men.

Read HbA1c with your blood count in mind. It reads falsely low when red cell survival is shortened and falsely high in iron deficiency anaemia.

Start with muscle and walking. Resistance training builds the tissue that stores most of your glucose, and walking after meals blunts the spike. Both are free and both move this.

Retest at three months after a real change. Insulin sensitivity recovers over months, so testing sooner mostly measures noise.

Where the paid report goes further

This page covers what the published evidence says in general. It cannot tell you what it means for you, because it does not know your medications, your labs, your history, or your dose.

A paid research report does that work. Jess builds it around your actual situation, walks the citations, and writes what the evidence supports for someone in your position. The brief is the shorter version. The deep dive is the one where every citation is read and the reasoning is laid out end to end, and Jess reviews every deep dive personally before it goes out.

Neither is medical advice, and neither replaces your prescriber. What they replace is the evening you would otherwise spend trying to work out which of forty search results is telling you the truth.