Prediabetes means blood sugar is higher than normal but not yet high enough to be called type 2 diabetes. It is a warning stage: the body is becoming resistant to insulin, and without change a meaningful share of people go on to develop diabetes within a few years. Because it sits on a spectrum, it can move either way — toward diabetes if nothing changes, or back to normal glucose if it does. It is also very common and, according to the CDC, most people who have it do not know. It causes few or no symptoms, so it is confirmed by numbers rather than feelings — an HbA1c of 5.7–6.4% or a raised fasting glucose makes the diagnosis.
Who is at risk
Prediabetes clusters with the features of insulin resistance. The main risk factors are:
- Excess weight, especially around the middle, and a mostly inactive lifestyle.
- Age 35 and over, when screening is generally advised, and a family history of type 2 diabetes.
- A history of gestational diabetes, or having given birth to a large baby.
- Polycystic ovary syndrome (PCOS), which is closely tied to insulin resistance.
- High blood pressure and an unfavorable lipid profile — low HDL cholesterol, high triglycerides.
- Certain ethnic backgrounds (South Asian, Hispanic, African, Indigenous and Pacific Islander) that carry higher risk at a given weight, and poor sleep or sleep apnea.
Symptoms
The defining feature of prediabetes is that it usually causes nothing at all — which is exactly why it is dangerous and why routine testing finds most cases. When there are clues, they are subtle: increased thirst, needing to urinate more often, unexplained fatigue, or slow-healing cuts. A telling sign in some people is acanthosis nigricans — soft, darkened, velvety skin in the neck folds or armpits — a visible marker of insulin resistance, and skin tags often keep it company. As glucose creeps toward the diabetic range, tingling or numbness in the hands and feet can appear, and high sugar is one of the causes worth checking behind night leg cramps. Because the condition is silent, do not wait for symptoms; if a symptom is your reason for testing, the symptoms hub links each one to its checklist.
Which lab tests confirm it
Prediabetes is defined by thresholds, so the tests and their cut-offs matter.
HbA1c reflects average blood sugar over roughly three months and needs no fasting, which makes it the most convenient test. The ADA range for prediabetes is 5.7–6.4% (39–46 mmol/mol); 6.5% or above signals diabetes. Because HbA1c depends on red cells living a normal lifespan, anemia, recent blood loss, pregnancy and some inherited hemoglobin variants can distort it — situations where a glucose-based test is trusted instead.
Glucose, measured fasting, is the classic test. A fasting value of 100–125 mg/dL (5.6–6.9 mmol/L) is impaired fasting glucose; 126 mg/dL (7.0 mmol/L) or higher, confirmed, is diabetes. “Fasting” means no food or calorie-containing drinks for at least eight hours, usually overnight — a casual daytime glucose is not used to diagnose prediabetes. If your lab reports in mmol/L, a unit converter lines the numbers up. (The WHO starts its impaired-fasting band a little higher, at 6.1 mmol/L.)
Glucose tolerance test — the OGTT — is the most sensitive option: you drink a measured glucose load and blood is checked at two hours. A result of 140–199 mg/dL (7.8–11.0 mmol/L) is impaired glucose tolerance; 200 (11.1 mmol/L) or more is diabetes. It catches cases a fasting test misses, but because it is more involved — a fasting morning draw, a sugary drink, then a second draw two hours later — it is used selectively rather than for everyone.
Insulin and HOMA-IR do not diagnose prediabetes but explain it. Fasting insulin, and the HOMA-IR value calculated from insulin and glucose together, estimate how resistant the body has become — helpful context, though without a universal cut-off.
Order of testing: HbA1c or fasting glucose is the usual first step; an OGTT is added when those are borderline or risk is high. Any abnormal result is confirmed on a second test before the label is applied.
How to read the results together
- Straightforward prediabetes: an HbA1c of 5.7–6.4% or a fasting glucose of 100–125 mg/dL, confirmed on repeat, with no diabetic-range value.
- Tests that disagree: HbA1c normal but the 2-hour OGTT in the impaired range (or the reverse). The tests measure different things, so the more abnormal one usually wins and prompts a repeat; conditions affecting red cells can make HbA1c misleading.
- Prediabetes with clear insulin resistance: borderline glucose plus a high fasting insulin and raised HOMA-IR, often alongside central weight gain and a high-triglyceride, low-HDL pattern — a stronger push toward early lifestyle change.
- A single high reading: one abnormal value is not a diagnosis. Unless glucose is clearly in the diabetic range with symptoms, the result is repeated — ideally with the same test — before prediabetes or diabetes is confirmed.
What happens next
Prediabetes is one of the most reversible findings in medicine, and the response is lifestyle first. Landmark prevention programs show that losing about 7% of body weight and doing roughly 150 minutes of moderate activity a week cut the risk of progressing to type 2 diabetes by more than half — often enough to return glucose to normal. The benefit is real and durable: in those trials the combination outperformed medication for most people and kept working for years. Practical steps are steady: more vegetables, whole grains and fiber; fewer sugary drinks and refined carbohydrates; regular movement that mixes walking with some strength work; and better sleep. A realistic first target is a few percent of body weight over several months rather than a crash diet, because small, sustained changes hold far better than short bursts. Your doctor rechecks HbA1c or glucose about once a year to track the trend, and in higher-risk people may discuss a medicine such as metformin to help prevent diabetes — most often when risk is high or glucose keeps rising, a decision they individualize, with no doses to self-manage here. Even people whose glucose returns to normal keep a higher lifetime risk, so it is worth staying with that annual check rather than assuming the matter is closed. Prediabetes rarely travels alone — it clusters with higher blood pressure, an unfavorable cholesterol pattern and extra weight around the middle — so the same changes that lower glucose also cut cardiovascular risk, which is where most of the long-term danger actually lies. Addressing blood pressure and cholesterol at the same time protects the heart, since these travel together.
When to see a doctor
Prediabetes itself is not an emergency, but some signs mean sugar may already be high. See a doctor promptly for marked thirst, frequent urination, blurred vision, or unexplained weight loss — features of diabetes rather than prediabetes. Very high thirst with drowsiness, nausea or confusion needs urgent care. Otherwise, the key action is not to ignore a borderline result: book a review to confirm it, set a plan, and agree when to retest, so a warning stage does not quietly become diabetes.
