What Does HbA1c Measure?
When blood glucose is elevated, glucose molecules permanently attach (glycate) to haemoglobin — the protein inside red blood cells that carries oxygen. Because red blood cells live for approximately 90 days, the HbA1c result reflects how much sugar has been in the bloodstream over the past 3 months — not just what you ate today. This makes it far more informative than a single fasting glucose reading, which captures only a snapshot. HbA1c does not require fasting and can be collected at any time of day, making it a practical tool for both diagnosing and monitoring diabetes.
Understanding Abnormal Results
⬆️ High HbA1c may indicate:
48–57 mmol/molNewly diagnosed diabetes — requires treatment initiation and lifestyle review
58–75 mmol/molPoorly controlled diabetes — increased risk of eye, kidney, and nerve damage
>75 mmol/molVery poor control — immediate intensification of treatment required; high complication risk
⬇️ Low HbA1c may indicate:
<30 mmol/mol in a diabetic on treatmentPossible over-treatment or hypoglycaemia risk — medication dose review needed
Frequently Asked Questions
Is HbA1c the same as a blood sugar test?
No — they measure different things. A fasting blood glucose (FBG) measures the exact glucose level in your blood at that moment, after fasting. HbA1c measures the accumulated effect of blood glucose over 3 months. Both are used together for a complete picture: FBG reflects day-to-day control, HbA1c reflects long-term patterns. A person can have a "good" fasting glucose but a high HbA1c if they have significant post-meal glucose spikes.
Can HbA1c be falsely normal or falsely high?
Yes. HbA1c is unreliable in conditions that affect red blood cell lifespan: sickle cell disease or trait (common in Nigeria — red cells turn over faster, giving falsely low HbA1c), iron deficiency anaemia (falsely high), haemolytic anaemia (falsely low), and recent blood transfusion (falsely low). In these situations, fasting glucose and OGTT are used instead.
How often should I have my HbA1c checked?
For people with diabetes: every 3 months until blood sugar is well controlled, then every 6 months. For pre-diabetes: every 6–12 months to monitor whether it is progressing, stable, or improving. For screening high-risk individuals without symptoms: annually from age 40 (or earlier with risk factors).
Does HbA1c reflect my diet this week?
No — that is the key difference from a fasting glucose test. HbA1c reflects the average of the past 2–3 months. You cannot manipulate it by eating well for a few days before the test. This makes it a more honest reflection of your actual blood sugar management over time.