HbA1c Blood Test
An HbA1c test measures your average blood sugar levels over the previous two to three months. It is one of the key tests used to screen for diabetes, assess pre-diabetes and monitor long term blood sugar control. HbA1c is commonly included in routine health checks, metabolic reviews and the investigation of symptoms related to energy levels, thirst or urination.
What the HbA1c Test Measures
HbA1c reflects the percentage of haemoglobin coated with glucose. It provides a stable indication of long term blood sugar control, unlike a fasting glucose which shows a single moment in time.
Typical HbA1c thresholds:
- Normal: below 42 mmol/mol
- Pre-diabetes: 42 to 47 mmol/mol
- Diabetes: 48 mmol/mol or above, confirmed by repeat testing unless symptoms are present
These ranges help identify early blood sugar problems and guide ongoing diabetes management.
Why the HbA1c Test Is Used
HbA1c helps identify:
- Early changes in blood sugar control
- Pre-diabetes
- Type 2 diabetes
- Long term diabetes control
- Risk of diabetes-related complications
- Treatment response to lifestyle change or medication
It is often paired with cholesterol tests, kidney function markers and liver tests as part of a metabolic health assessment.
Common Reasons to Have an HbA1c Test
This test may be arranged if you have:
- Increased thirst
- Frequent urination
- Fatigue or low energy
- Family history of diabetes
- Weight gain or central weight distribution
- Raised cholesterol
- High blood pressure
- Polycystic ovary syndrome (PCOS)
- Concern about long term sugar intake or metabolic health
People with diabetes usually have HbA1c checked every three to six months depending on treatment needs.
Understanding HbA1c Patterns
Higher HbA1c
Often linked to long term elevated blood sugar. Causes may include reduced insulin sensitivity, lifestyle factors, certain medicines or undiagnosed diabetes. Very high HbA1c levels can sometimes reflect reduced insulin production from the pancreas, although this is not a diagnostic test for pancreatic disease.
Borderline or pre-diabetic HbA1c
Indicates increased risk of developing diabetes. Lifestyle changes at this stage are often very effective.
Lower HbA1c
May relate to strict blood sugar control, weight loss, medication effects or, rarely, conditions affecting red blood cells.
Temporary fluctuations
Illness, red blood cell disorders, anaemia or rapid changes in blood sugar can influence results.
How the Test Is Performed
A small blood sample is taken from a vein in your arm. No fasting is required. Results are typically ready within 24 to 48 hours.
When to Discuss HbA1c Results with a GP
Speak to a GP if:
- Your HbA1c is in the pre-diabetic or diabetic range
- You have symptoms of high blood sugar
- You have long term conditions such as high blood pressure or cholesterol issues
- You are making lifestyle changes and want to review progress
A GP can provide personalised advice, treatment options and metabolic health planning.
Related Tests and Articles
HbA1c is often reviewed alongside:
- Full blood count
- Liver function tests
- Lipid profile
- Kidney function tests
- Thyroid function tests
- Blood pressure review
- Urine testing for protein (for diabetes monitoring)
For a wider overview of routine blood markers, you can visit our main Blood Tests section in the Knowledge Base.
If you would like to discuss HbA1c results or any concerns about your metabolic health, you can book an online GP appointment for clear and personalised advice.
Last reviewed by Dr Zamiel Hussain, GMC registered GP
Updated: 8 December 2025