For clinicians

HbA1c

Unit
%

What is HbA1c?

HbA1c shows how high your blood sugar was on average over the past two to three months. Sugar in your blood binds to haemoglobin, the red pigment in your blood cells. The higher your average blood sugar, the more sugar sticks to it and the higher your HbA1c.

Clinical frame

HbA1c reflects the average glycaemia of the past two to three months and is an important parameter for the diagnosis and follow-up of prediabetes and diabetes [3].

In the context of insulin resistance, however, HbA1c is above all a later marker of metabolic dysregulation. Insulin resistance and compensatory hyperinsulinaemia can be present for years while the beta cell still keeps glycaemia within normal limits [1]. A normal HbA1c therefore does not rule out insulin resistance.

When HbA1c starts to rise, this indicates that the compensation is becoming insufficient to keep glucose regulation fully normal. For the early detection of insulin resistance, markers such as HOMA-IR, the TyG index and triglycerides/HDL are therefore more sensitive [1].

HbA1c must always be interpreted in its clinical context. Conditions that affect the lifespan of erythrocytes or the composition of haemoglobin, such as anaemia, blood loss, kidney disease and haemoglobinopathies, can distort the value [2] [3].

What moves this value?

HbA1c responds slowly: it reflects weeks, not days. What helps most: fewer fast sugars and heavily processed carbohydrates, more fibre, more exercise (even a short walk after a meal counts), a healthy weight and enough sleep.

Expect a visible effect on this value only after two to three months; that is normal and not a sign that your effort is not working.

What this connects

Developed and reviewed with the Synapse medical advisory board.

References

  1. Roden, M. & Shulman, G. I. The integrative biology of type 2 diabetes. Nature 576, 51–60 (2019). doi.org/10.1038/s41586-019-1797-8
  2. Bruhn, L. et al. Physiological factors contributing to HbA1c in the normal and pre-diabetic range: a cross-sectional analysis. Endocrine 68, 306–311 (2020). doi.org/10.1007/s12020-020-02234-3
  3. American Diabetes Association Professional Practice Committee. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes-2026. Diabetes Care 49, S27–S49 (2026). doi.org/10.2337/dc26-S002

The colour zones are personal: they depend on age, sex, risk and history, and appear in the patient's own report.

Insights to discuss with the patient, not a diagnostic instrument.