What the value means
HbA1c (glycated haemoglobin) reflects your average blood sugar over roughly the past 2–3 months. A value of 5.8% corresponds to 40 mmol/mol. Prediabetes thresholds are not uniform: the American Diabetes Association uses 5.7–6.4% (39–47 mmol/mol), a WHO expert group considers 6.0–6.4% as high risk, and laboratory reference ranges differ. Diabetes is diagnosed from 6.5% (48 mmol/mol), confirmed by repeat testing. From a prevention point of view, though, the risk of diabetes and vascular disease rises gradually already within the upper part of the “normal” range. The result can also be skewed by iron deficiency, anaemia, kidney disease, recent blood loss or certain haemoglobin variants.
Possible causes
- Reduced insulin sensitivity – most often linked to abdominal fat, lack of exercise and a sedentary lifestyle.
- Diet – plenty of sugary drinks and refined carbohydrates, little fibre.
- Sleep and stress – short sleep and chronic stress impair blood sugar control.
- Genetics and age – diabetes in the family and older age raise the risk.
- Measurement bias – iron deficiency can falsely raise HbA1c.
What you can do
- Further tests – fasting glucose, possibly insulin, and an oral glucose tolerance test if your doctor recommends it.
- Exercise – at least 150 minutes of brisk activity per week plus two strength sessions; a short walk after meals also helps.
- Weight – if you are overweight, losing 5–7% substantially slowed progression to diabetes in clinical trials.
- Diet – vegetables, legumes, whole grains and enough protein; limit sugary drinks and white bread.
- Follow-up – repeat HbA1c in 3–6 months to see whether the changes are working.
When to see a doctor
Discuss the result with your GP, especially if you are overweight or have high blood pressure, raised blood lipids, a family history of diabetes or a history of gestational diabetes. Seek medical attention promptly if you experience thirst, frequent urination, unexplained weight loss or blurred vision.