What HbA1c measures
HbA1c shows how much glucose has attached to the haemoglobin in your red blood cells. Red cells live for about three months, so the result reflects your average blood sugar over roughly the last 2 to 3 months, with the most recent weeks counting a little more. You do not need to fast for the test.
What the numbers mean
| HbA1c | Usual meaning |
|---|---|
| Below 5.7% | Normal |
| 5.7% to 6.4% | Prediabetes |
| 6.5% or higher | In the diabetes range (confirmed with a repeat test or a glucose test) |
For someone already living with diabetes, the HbA1c is also a rough guide to average glucose:
| HbA1c | Average glucose (approx.) |
|---|---|
| 6% | about 126 mg/dL |
| 7% | about 154 mg/dL |
| 8% | about 183 mg/dL |
| 9% | about 212 mg/dL |
What is a good target?
For many adults with diabetes, a target below 7% is common. But the right target is personal. It can be lower for a young person with a short history of diabetes, and higher for someone who has frequent low sugars, other serious illnesses or a limited life expectancy. Your target should be agreed with your doctor.
When HbA1c can mislead
HbA1c depends on healthy red blood cells, so it can read falsely high or low when:
- you have anaemia or iron deficiency;
- you have recently had blood loss or a transfusion;
- you carry a haemoglobin variant or thalassaemia trait;
- you have advanced kidney disease or liver disease;
- you are pregnant.
It also hides the ups and downs. Two people can both have an HbA1c of 7% while one has steady sugars and the other swings between highs and lows.
How often should it be checked?
Usually every 3 months when treatment is changing or sugars are not at target, and about every 6 months when diabetes is stable. Your doctor may advise a different schedule.
HbA1c and continuous glucose monitoring
A continuous glucose monitor (CGM) shows your glucose through the day, including nights and after meals. It shows how much time you spend in your target range and when lows occur, which HbA1c cannot. The two measures work best together.
When to see a specialist
Consider an endocrinology opinion if your HbA1c stays high despite treatment, you have frequent low sugars, your readings do not match your HbA1c, or you were recently diagnosed and want a clear plan.
When can HbA1c be misleading?
HbA1c depends on how long red blood cells circulate, not just on glucose. Iron-deficiency anaemia, haemolysis, recent bleeding or transfusion, some haemoglobin variants, pregnancy and advanced kidney disease can make the result differ from the actual glucose pattern. The direction and size of the effect depend on the condition and assay.
If HbA1c does not match home glucose readings or a continuous glucose monitor, do not assume either result is automatically wrong. Your clinician may review the blood count, kidney function, assay method and glucose records, or use plasma glucose testing or another marker when appropriate.
Does one result confirm diabetes?
In someone without clear symptoms or a hyperglycaemic emergency, an abnormal diagnostic result generally needs confirmation with a repeat test or a second abnormal test. HbA1c is one way to diagnose diabetes, but it is not suitable for every person or every clinical situation.
This guide is for general educational purposes and does not replace individual medical advice, diagnosis or treatment. Consult your doctor for advice specific to your health. Do not change your medicines based on an HbA1c result without talking to your doctor.