Updated 13 August 2026 · 6 min read
Prediabetes is one of the more confusing labels in medicine. It is not a disease in the usual sense, it produces no symptoms in most people, and the name implies an inevitability that the evidence does not support. It is worth understanding on its own terms.
Prediabetes describes blood glucose that is above the normal range but below the threshold used to diagnose diabetes. Three tests can establish it, and only one of them needs to be in range:
| Test | Prediabetes range |
|---|---|
| Fasting plasma glucose | 100 – 125 mg/dL (5.6 – 6.9 mmol/L) |
| A1C | 5.7% – 6.4% |
| 2-hour oral glucose tolerance test | 140 – 199 mg/dL (7.8 – 11.0 mmol/L) |
The three do not always agree with each other. Someone can have a fasting glucose in the normal range and an A1C in the prediabetes range, or the reverse. They are measuring related but different things — a single point, an average, and a challenge response respectively.
The classic symptoms of high blood glucose — excessive thirst, frequent urination, blurred vision, unexplained weight loss — appear when glucose is substantially elevated. Prediabetes sits well below that level.
The result is that it is nearly always found incidentally: routine blood work, a pre-operative check, an insurance screening. A large share of people who meet the criteria do not know they do, and there is no sensation that would tell them.
Prediabetes raises the probability of developing type 2 diabetes. It does not determine it. A meaningful proportion of people with prediabetes return to normal glucose levels; others remain in the range for many years without progressing.
Where in the range someone sits matters. Values close to the diabetes threshold carry higher risk than values just over the normal line, and being in range on more than one test carries more weight than being in range on one.
It is also worth knowing that elevated glucose short of diabetes is associated with increased cardiovascular risk in its own right, which is part of why it gets attention rather than being dismissed as a near-miss.
The best-known trial here is the Diabetes Prevention Program, a large randomised study in the United States comparing an intensive lifestyle programme against metformin against placebo, in adults at high risk.
Over roughly three years, the lifestyle arm reduced progression to type 2 diabetes by about 58% compared with placebo. Metformin reduced it by about 31%. The lifestyle intervention outperformed the medication, and the difference was largest in older participants.
The lifestyle programme was specific rather than vague: a target of losing around 7% of body weight, and at least 150 minutes a week of moderate activity, supported by structured coaching over time. Follow-up studies found some of the benefit persisted years after the programme ended.
Two things are worth taking from this. The first is that progression is genuinely modifiable — this is not a diagnosis you simply wait out. The second is that the intervention that produced those numbers was substantial and supported. It was not a leaflet.
Prediabetes is a risk marker, not a sentence. It is silent, it is common, it is usually found by accident, and the largest trial in the field showed that progression can be substantially reduced. The most useful response is neither panic nor dismissal — it is finding out your actual number and putting a recheck in the calendar.
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