Haemoglobin A1c (HbA1c)
Also known as: A1c, Glycated haemoglobin, Glycosylated haemoglobin
HbA1c reflects your average blood glucose over the past 2–3 months by measuring how much glucose has permanently attached to haemoglobin. It is the gold-standard test for diagnosing and managing diabetes.
Venous blood (EDTA tube)
4–8 hours
Not required
Diabetes & Blood Sugar
Reference Ranges
| Measurement | Reference Range | Unit |
|---|---|---|
| Normal | ≤ 5.6 | % |
| Pre-diabetes | 5.7 – 6.4 | % |
| Diabetes | ≥ 6.5 | % |
| Target (managed diabetes) | ≤ 7 | % |
Reference ranges are typical adult values. Your laboratory may use slightly different intervals — always use your lab's reported reference.
What This Test Measures
When glucose circulates in the blood, it binds irreversibly to haemoglobin in red blood cells — a process called glycation. Because RBCs live about 90 days, the percentage of glycated haemoglobin (HbA1c) represents an integrated picture of glucose control over that period. A 1% change in HbA1c corresponds to roughly 28 mg/dL change in average glucose.
When Is This Test Ordered?
- Diagnosing type 2 diabetes or pre-diabetes
- Monitoring glycaemic control in known diabetics (every 3–6 months)
- Assessing cardiovascular risk in metabolic syndrome
- Evaluating whether current diabetes medication is effective
When Results Are High
Above 6.5% confirms diabetes diagnosis. Above 9% indicates poorly controlled diabetes with high risk of complications including neuropathy, retinopathy, and nephropathy. Each 1% reduction in HbA1c reduces diabetes complications by ~25% (UKPDS data).
When Results Are Low
Below 4% is very rare and suggests conditions that shorten RBC lifespan (haemolytic anaemia, sickle cell disease) or laboratory error — not simply 'extra good' glucose control.
Converting A1c to estimated average glucose (eAG)
| A1c (%) | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|
| 5 | 97 | 5.4 |
| 6 | 126 | 7.0 |
| 7 | 154 | 8.6 |
| 8 | 183 | 10.2 |
| 9 | 212 | 11.8 |
| 10 | 240 | 13.4 |
When A1c misleads — and what to use instead
In conditions that alter RBC lifespan or haemoglobin structure, HbA1c gives unreliable results. Fructosamine reflects the past 2–3 weeks of glucose control and is a useful alternative for people with haemoglobin variants or rapid RBC turnover. Continuous glucose monitoring (CGM) provides real-time glucose data that complements — but does not yet replace — A1c in clinical guidelines.
Factors That Can Affect Your Result
- Haemolytic anaemia falsely lowers A1c (shorter RBC lifespan)
- Iron deficiency anaemia can falsely raise A1c
- Sickle cell trait may give falsely low results with some assay methods
- Pregnancy (especially third trimester) lowers A1c due to higher RBC turnover
Tracking This Test Over Time
The most important trend is the direction — a rising A1c from 5.9% to 6.3% over 18 months means you are progressing toward diabetes regardless of whether either result crossed a diagnostic threshold. Act on the slope, not just the single value.
Track your HbA1c in LoomsRelated Tests
FBG
Fasting blood glucose is the simplest, most widely used test for diabetes screening. Measured after at least 8 hours without food, it reflects your baseline blood sugar control before any meal stimulus.
CMP
The CMP is a 14-test panel covering glucose, electrolytes, kidney function, and liver enzymes in a single draw. Most adults have at least one CMP a year as part of routine check-ups.
Medical disclaimer
This page is for educational purposes only and does not constitute medical advice. Reference ranges vary between laboratories, and results must be interpreted in the context of your symptoms, history, and other tests. Always discuss your results with your healthcare provider. Content reviewed by the Looms medical team, 2026-06-01.