Short answer: HbA1c (glycated haemoglobin, or A1c) measures how much of your haemoglobin has glucose attached to it. Because red cells live for about three months, it reflects your average blood sugar over the previous two to three months, not the moment of the test. It is reported as a percentage (common in the US) or in mmol/mol (the international IFCC unit used in the UK and much of Europe).
At a glance
| Measures | The share of haemoglobin with glucose attached |
|---|---|
| Reflects | Average blood sugar over the previous two to three months |
| Units | % (US) or mmol/mol (IFCC, UK and Europe) |
| Conversion | mmol/mol = (% − 2.15) × 10.929 |
| LOINC | 4548-4 |
| Can be misleading | Anaemia, recent blood loss or transfusion, haemoglobin variants, pregnancy, kidney disease |
What the test measures
Glucose in the blood sticks slowly and permanently to haemoglobin. The higher the average glucose, the larger the share of haemoglobin that is "glycated". The test does not need fasting and is not changed by a single meal, which is why it is used both to diagnose diabetes and to follow it over time.
Some conditions change the life of red cells (anaemia, recent blood loss or transfusion, some haemoglobin variants, pregnancy, advanced kidney disease) and can make HbA1c read higher or lower than the real average. Laboratories and doctors know these limits; tell your doctor if one applies to you.
When it is ordered
Common reasons, which your doctor adapts to you:
- as a screening or diagnostic test for diabetes;
- every few months for people with diabetes, to follow the average over time;
- before and after a change of treatment or lifestyle.
How the result is written on the report
| Result on the report | LOINC code | Usual unit | Also seen as |
|---|---|---|---|
| HbA1c | 4548-4 | % | mmol/mol (IFCC) |
| Fasting glucose (often on the same report) | 1558-6 | mg/dL | mmol/L |
The two units are linked by a fixed formula: mmol/mol = (% − 2.15) × 10.929. For example, 6.0 % ≈ 42 mmol/mol, 7.0 % ≈ 53 mmol/mol, 8.0 % ≈ 64 mmol/mol. Many reports print both. The lab unit converter does the conversion for you.
Reading your report
International bodies such as the WHO and the American Diabetes Association use 6.5 % (48 mmol/mol) as one of the thresholds for diagnosing diabetes, confirmed by a repeat test; your individual target, if you have diabetes, is agreed with your doctor and can be different. Because HbA1c moves slowly, a change shows best when results are compared every three months or more, in the same unit.
Keeping the results in your record
Scan or photograph the report in Anpheros Daily: each value is read with its unit and the laboratory's reference range, you check it, and it is stored with its LOINC code as an HL7 FHIR Observation, a format used by many hospitals and national health systems. Results from different laboratories line up on one chart over time, and the lab unit converter helps when two reports use different units. Our guide on how to read lab results explains reference ranges and flags in general; the lab results guide for a new doctor shows how to share them.
What this page does not do
It explains what the test is and how the result is written. It does not interpret your result, diagnose or recommend treatment: the meaning of a value depends on your history, your other results and how the sample was taken, and that is your doctor's job.
Related pages
- Fasting blood glucose test
- Lipid panel (cholesterol test)
- Urine albumin-to-creatinine ratio (ACR, microalbumin)
Sources
Frequently asked questions
Do I need to fast for an HbA1c test?
No. HbA1c is not affected by what you ate before the test.
How do I convert HbA1c from % to mmol/mol?
Use mmol/mol = (% − 2.15) × 10.929. For example, 6.5 % is about 48 mmol/mol.
How often is HbA1c measured?
It depends on the reason. For people with diabetes it is often every three to six months; your doctor decides the interval.
Why is my HbA1c different from my glucose meter average?
They measure different things over different periods, and some conditions affecting red cells change HbA1c. Show both to your doctor rather than comparing them yourself.
Try it in Anpheros Daily
Photograph your lab report and Anpheros Daily lines up each value with its reference range, so you can compare reports from different laboratories.
How it works in the app →
Anpheros builds a medical record that the patient controls and can share with any clinic, on an HL7 FHIR R4 platform, based in the EU. These guides help you understand and organise your health; they do not replace your doctor.
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