Also Known As
Haemoglobin A1c
Glycated or glycosylated haemoglobin
Formal Name
This article was last reviewed on
This article waslast modified on 8 January 2021.
At a Glance
Why Get Tested?

To monitor average blood glucose levels in someone with diabetes and to help treatment decisions. It can also be used to make a diagnosis of type 2 diabetes and to identify prediabetes.

When To Get Tested?

When first diagnosed with diabetes and then at least twice a year

Sample Required?

A blood sample taken from a vein in the arm

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

Some of the glucose in your blood binds to haemoglobin (the protein that carries oxygen in your red blood cells). This combination of glucose and haemoglobin is called haemoglobin A1c (HbA1c). The amount of HbA1c formed is directly related to the average concentration of glucose in your bloodstream. Red blood cells live for 2–3 months, and because of this, the amount of HbA1c in your blood reflects the average level of glucose in your blood during the last 2-3 months. If your diabetes is not well controlled, your blood glucose levels will be high causing higher HbA1c levels.

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Common Questions
  • How is it used?

    The test for HbA1c shows how well your diabetes has been controlled over the last 2-3 months. Even though you may have some very high or very low blood glucose values, HbA1c will give a picture of the average level of glucose in your blood over that time period. The result can help you and your doctor understand if the measures you are taking to control your diabetes are working.

    In the past the test was only used to monitor blood glucose control in patients with known diabetes . Now the World Health Organisation (WHO) recommendsthat HbA1c can also be used to diagnose type 2 diabetes in people who were not previously known to have the condition. There are certain situations in which HbA1c cannot be used to diagnose diabetes. An oral glucose tolerance test would be used as an alternative.

  • When is it requested?

    The Department of Health recommends that everyone with diabetes has HbA1c measured at least twice a year. HbA1c may be measured more frequently in those who have just been diagnosed with diabetes, in those whose blood glucose remains too high, or when a treatment plan changes. The test can also be used to diagnose type 2 diabetes. Please speak to your healthcare professional about local guidelines that may be in place, as there maybe variations in local procedures., and there are certain groups of patients in which HbA1c cannot be used to diagnosis diabetes.

  • What does the test result mean?

    If you have diabetes and your HbA1c is below 48 mmol/mol it is likely that your diabetes is well controlled. If your HbA1c rises above 48 mmol/mol, you are at increased risk of developing long term complications such as eye disease, kidney disease or nerve damage. It is worth noting that some people can find it difficult to get their HbA1c down to 48 mmol/mol without experiencing frequent episodes of hypoglycaemia (low blood sugar), and if this is the case, the target HbA1c may be higher than 48 mmol/mol.

    The World Health Organisation (WHO) suggests the following diagnostic guidelines for diabetes:

    • HbA1c below 42 mmol/mol: Not diabetes
    • HbA1c between 42 and 47 mmol/mol: Impaired glucose regulation or prediabetes.
    • HbA1c of 48 mmol/mol or over: type 2 diabetes.
  • Is there anything else I should know?

    If you have an uncommon type of haemoglobin, known as a haemoglobin variant (for example thalassaemia or sickle cell disease) , accurate results will depend on the method used to measure HbA1c. If you have haemolytic anaemia or heavy bleeding, your test results may be falsely low. If you are iron deficient, this may raise your HbA1c result. HbA1c is not used for diagnosis of diabetes during pregnancy.

  • Is there a home test for HbA1c?

    Yes. HbA1c could be measured at home but this is rarely done, is expensive and should not be necessary if you are being monitored by your doctor.

  • Are all HbA1c tests the same?

    All HbA1c methods are now standardised to an IFCC reference material, and are reported in mmol/mol standard units. Therefore, results generated by different laboratories are traceable to this global standard, and comparable.