HbA1c
Also known as: glycated haemoglobin, haemoglobin A1c
The fraction of haemoglobin that has glucose stuck to it. Because red cells live about 120 days, it reports the average blood glucose over the previous two to three months in a single number.
- Canonical name
- Glycated haemoglobin
- Abbreviations
- HbA1c, A1c
- Kind
- Laboratory test
- Categories
- Diabetes & glucose
- Specimen
- Whole blood (EDTA)
- Method
- Immunoassay, Chromatography and mass spectrometry
- Terminology
- LOINC 4548-4
- Type
- Blood test
- Sample
- Blood from a vein, no fasting
- Used for
- Diagnosing type 2 diabetes, monitoring diabetes control
- Measures
- Glycated haemoglobin, the average blood glucose of the previous two to three months
- Result
- Numeric, read against diagnostic and target thresholds
Why is it used?
- Diagnosing type 2 diabetes
- Monitoring diabetes control every 3-6 months
- Setting and reviewing treatment targets
What does it measure?
| Component | What it measures | A higher value may be seen in | A lower value may be seen in |
|---|---|---|---|
| HbA1c (glycated haemoglobin) HbA1c HbA1c | Percentage of haemoglobin with glucose attached, reported in mmol/mol | Diabetes, prediabetes; falsely high with iron deficiency and slow red-cell turnover | Improving control; falsely low with haemolysis, blood loss, transfusion, pregnancy |
A high or low value can be associated with several different situations; the result is interpreted with other results, symptoms, history and clinical findings.
How is it performed?
Venous blood, no fasting.
Specimen. Venous blood in an EDTA tube; fingerprick point-of-care devices in some clinics
Do I need to prepare?
None.
What do the results generally mean?
| Finding | What it may indicate |
|---|---|
| 48 mmol/mol or above | Diabetes (if no condition affecting red cells) |
| Target 48-58 in treated diabetes | Individualised: tighter in the young and newly diagnosed, looser in the frail |
| Falling value | Treatment and lifestyle changes are working |
Guideline thresholds
| Threshold | Value | Unit | Applies to | Country · source |
|---|---|---|---|---|
| Diabetes | 48 or above | mmol/mol (6.5%) | Diagnosis of type 2 diabetes; repeated to confirm unless symptoms are present. Not valid in conditions that affect red cells | UK UK |
| Non-diabetic hyperglycaemia (prediabetes) | 42 to 47 | mmol/mol (6.0-6.4%) | High risk of type 2 diabetes; lifestyle intervention offered | UK UK |
| Treatment target (diet or a single drug not causing hypoglycaemia) | 48 | mmol/mol (6.5%) | Adults with type 2 diabetes managed by lifestyle or one agent; individualised | UK UK |
| Treatment target (a drug that can cause hypoglycaemia) | 53 | mmol/mol (7.0%) | Adults with type 2 diabetes on treatment associated with hypoglycaemia; relaxed for older or frail people | UK UK |
Clinical decision thresholds come from the named guideline and country; they are not laboratory reference intervals, and they change when guidance changes.
What can affect the result?
- Anything that shortens or lengthens red-cell life: haemolysis, blood loss, transfusion, iron deficiency, kidney failure, pregnancy
- Haemoglobin variants, which interfere with some assay methods
- Very recent changes in glucose control, which the value has not yet caught up with
- Erythropoietin and iron treatment
Medicines. Glucose-lowering medicines lower it; corticosteroids and some antipsychotics raise it by raising glucose; iron and erythropoietin treatment can shift it independently of glucose.
What can the test not tell you?
- Day-to-day swings in glucose or episodes of hypoglycaemia
- Type 1 diabetes at presentation, where glucose rises too fast for HbA1c to reflect it
- Whether control is good in someone whose red cells turn over abnormally
Unreliable when red cell life is abnormal: anaemia, haemoglobin variants, recent transfusion, pregnancy, kidney failure. Not for diagnosing type 1 diabetes, which moves too fast.
Other tests commonly used with it
Medicines monitored with this test
Each medicine page cites the official document that names this test in its monitoring plan.