Insulin resistance develops 10 to 20 years before your blood sugar rises enough for an HbA1c test to catch it. By the time the NHS detects prediabetes, your metabolism has been impaired for years. Fasting insulin and HOMA-IR catch it at the stage where it's still fully reversible. The NHS tests neither.
CPRD analysis of UK electronic health records estimated approximately 5 million adults aged 16 and over in England had non-diabetic hyperglycaemia (NDH) in 2015, a prevalence of 11.4%. The NHS Diabetes Prevention Programme reports England-wide NDH prevalence of 10.7% (95% CI 10.2 to 11.1%). NICE NG28 defines NDH as HbA1c 42 to 47 mmol/mol or fasting glucose 5.5 to 6.9 mmol/L.
The Lancet Regional Health (2022) reports that 7% of people with prediabetes progress to type 2 diabetes within the first year. Among those with obesity and NDH, the annual progression rate rises to 11%. Every year of undetected insulin resistance makes reversal harder and progression more likely.
But the 5 million figure only captures people whose HbA1c has already risen into the prediabetic range. It does not include the potentially millions more with insulin resistance whose HbA1c is still "normal." These people are metabolically impaired, gaining weight, feeling tired, crashing after meals, and have no idea why because the only test their GP runs has not caught it yet.
Diabetes does not happen overnight. It develops over a decade or more through a predictable sequence. Each stage is detectable by a different test. The NHS only uses the last one.
The entire top half of this timeline is invisible to the NHS. Fasting insulin and HOMA-IR detect the problem at stages 1 and 2, when reversal through diet, exercise, and lifestyle change is straightforward. HbA1c only flags it at stage 3, after a decade of metabolic damage. The difference between catching insulin resistance at year 2 versus year 12 is the difference between a lifestyle adjustment and a chronic disease.
HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) is calculated from fasting insulin multiplied by fasting glucose, divided by a constant. It is a validated surrogate marker for insulin resistance in non-diabetic individuals. Published research in Diabetologia and The Lancet Diabetes and Endocrinology confirms it can detect metabolic dysfunction before HbA1c or fasting glucose become abnormal.
General reference points: Below 1.0 is generally considered optimal. Between 1.9 and 2.9 suggests early insulin resistance. Above 2.9 is associated with metabolic syndrome criteria in most research frameworks.
Important limitations: HOMA-IR does not have a validated UK diagnostic cut-off. It is not recommended as a standalone screening test by the American Diabetes Association, NICE, or any major diabetes guideline. Different laboratories use different insulin assays, which can affect the calculation. It should not be used in patients with overt diabetes where beta-cell function is already impaired. It is a research and clinical adjunct tool, not a standalone diagnostic.
How TrueVitals uses it: We report HOMA-IR as an early metabolic warning marker alongside HbA1c, fasting glucose, C-peptide, fructosamine, and triglycerides. It provides context that HbA1c alone cannot. If your HOMA-IR is elevated, our report recommends discussing the finding with your GP and provides specific dietary, exercise, and lifestyle recommendations that target insulin sensitivity. We do not use it to diagnose or label prediabetes. We use it to alert you to a metabolic trend that warrants attention.
This honest framing is important because some private providers overstate HOMA-IR's diagnostic power. It is a powerful early indicator. It is not a diagnosis. Treating it as one undermines its clinical utility and your trust.
Neither HbA1c nor HOMA-IR tells the complete metabolic story alone. The comprehensive picture requires both alongside several other markers that reveal the systems interacting with insulin resistance.
The lagging indicators. HbA1c shows your 3-month blood sugar average. Fasting glucose shows your blood sugar after an overnight fast. Both are late-stage markers: by the time they rise, insulin resistance has been present for years. But they are essential for tracking improvement and for formal NICE NG28 classification.
The early indicators. Fasting insulin rises years before glucose. HOMA-IR quantifies the resistance. Together they detect the metabolic dysfunction that HbA1c will eventually catch, but catch it a decade or more earlier when intervention is simplest and most effective.
Produced alongside insulin in equal amounts by the pancreas. C-peptide confirms how much insulin your pancreas is actually producing. Important for distinguishing insulin resistance (high production, poor cellular response) from declining pancreatic function (falling production, late-stage disease).
Elevated triglycerides with low HDL is a hallmark of insulin resistance and metabolic syndrome. The triglyceride-to-HDL ratio is an accessible surrogate marker for insulin resistance that appears on a standard lipid panel. Combined with fasting insulin, it builds a multi-angle metabolic picture.
Thyroid and metabolism are bidirectional. Hypothyroidism worsens insulin resistance. Insulin resistance impairs thyroid function. Testing both simultaneously reveals whether thyroid dysfunction is contributing to metabolic impairment. Thyroid blood test guide.
Chronic inflammation impairs insulin signalling directly. hs-CRP measures body-wide inflammation. Elevated CRP alongside insulin resistance indicates a compounding problem that dietary intervention alone may not resolve without addressing the inflammatory component.
You carry weight around your abdomen — central adiposity is the strongest visual correlate of insulin resistance
You crash after meals, especially carbohydrate-heavy ones — a classic sign of reactive hypoglycaemia from insulin overproduction
You can't lose weight despite consistent effort — high insulin physically prevents fat release from adipose tissue. See our weight loss guide.
You have a family history of type 2 diabetes — genetic predisposition means earlier monitoring is more important, not less
You have PCOS — insulin resistance underlies the majority of PCOS and directly disrupts ovulation and androgen levels. PCOS blood test guide.
You are starting or currently on Mounjaro, Wegovy, or another GLP-1 — baseline and ongoing metabolic monitoring is essential. Mounjaro blood test guide.
Your GP tested HbA1c and said it's normal — that means your blood sugar hasn't risen yet. It does not mean your insulin sensitivity is intact. It may have been deteriorating for years.
114 biomarkers including fasting insulin, HOMA-IR, HbA1c, C-peptide, and every metabolic marker that reveals insulin resistance years before standard tests. Results in 48 hours.
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