Prediabetes is a state in which blood glucose sits consistently above the normal range but below the threshold used to diagnose type 2 diabetes. It is defined entirely by lab numbers — fasting glucose, an oral glucose tolerance test, or HbA1c — and it usually produces no symptoms, so most people find out from a routine blood panel. It is best read as a warning stage rather than a disease, because a large share of people move back toward normal glucose once the cause is addressed.
What it measures
Three separate tests can establish the diagnosis, and they do not always agree. Fasting plasma glucose is drawn after eight to twelve hours without food and reads your blood glucose at that moment. The oral glucose tolerance test measures glucose two hours after you drink a standard 75 g glucose solution, which shows how quickly you clear a sugar load. The third test, Glycated hemoglobin (HbA1c), reads the share of your hemoglobin that has glucose bound to it and reflects average blood sugar over roughly the previous two to three months. One person can land in the prediabetes band on one test and the normal band on another, which is why a borderline result is normally repeated before anything is labeled.
Typical values
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting plasma glucose | below 100 mg/dL (5.6 mmol/L) | 100-125 mg/dL (5.6-6.9 mmol/L) | 126 mg/dL (7.0 mmol/L) or above |
| 2-hour oral glucose tolerance test | below 140 mg/dL (7.8 mmol/L) | 140-199 mg/dL (7.8-11.0 mmol/L) | 200 mg/dL (11.1 mmol/L) or above |
| HbA1c | below 5.7% (39 mmol/mol) | 5.7-6.4% (39-46 mmol/mol) | 6.5% (48 mmol/mol) or above |
Those are the American Diabetes Association bands, the ones most US labs print. Where the lower line falls differs between guidelines: the World Health Organization sets impaired fasting glucose at a higher starting point than 100 mg/dL, and several national bodies use a narrower HbA1c window, so the same result can be prediabetes in one country and normal in another. Units differ too — mg/dL in the United States, mmol/L across most of Europe.
Why it matters for longevity
Prediabetes matters for what it predicts and what travels with it. Cohort data link glucose in this range to a higher risk of type 2 diabetes, cardiovascular disease and all-cause mortality, and that risk rises gradually rather than switching on at a cut-off. The usual underlying driver is Insulin resistance, which usually arrives alongside a widening waist, higher triglycerides, higher blood pressure and fatty liver — the cluster known as metabolic syndrome. Progression is not a given: commonly cited estimates put annual conversion to type 2 diabetes in the mid-single digits to about ten percent, but that depends heavily on which test defined the diagnosis and on the population, and a meaningful share of people return to normal glucose. How the diagnosis is confirmed and how reversible it is are covered in more depth in the reference entry on Prediabetes.
What changes it
Body weight, muscle and daily movement move it most. In the US Diabetes Prevention Program, a structured lifestyle program built on modest weight loss and about 150 minutes of walking a week cut progression to type 2 diabetes by more than half over roughly three years, and beat metformin, which cut it by around a third. In practice that means cutting refined starch, added sugar and sugary drinks; walking for ten to fifteen minutes after meals, which blunts the post-meal rise; and strength training, since muscle is the largest disposal site for glucose. Sleep counts too: a few nights of short or broken sleep measurably worsen glucose tolerance in healthy people. Metformin is sometimes prescribed when risk is high or lifestyle change has not been enough — a decision for your clinician. Some risk factors are fixed: age, family history, ethnic background and a past pregnancy affected by gestational diabetes all raise your starting risk.
Related reading
- How to Improve Metabolic Health: A Practical Guide
- Which Blood Tests Reflect Aging and How to Read Them
- Heart Health: A Prevention Guide for Longevity
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.