When first diagnosed with diabetes and then at least twice a year
A blood sample taken from a vein in the arm
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.
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.
HbA1c used to be given in percentage units, but this changed in 2009. More information about the new way of reporting test results can be found here.
The World Health Organisation (WHO) suggests the following diagnostic guidelines for diabetes:
- HbA1c below 42 mmol/mol (6.0%): Not diabetes
- HbA1c between 42 and 47 mmol/mol (6.0–6.4%): Impaired glucose regulation or prediabetes.
- HbA1c of 48 mmol/mol (6.5%) 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?
Are all HbA1c tests the same?
On This Site
Tests: Glucose, Microalbumin
Elsewhere On The Web
Analyte Monographs alongside the National Laboratory Medicine Catalogue (AMALC): HbA1c
A change in reporting your HbA1c results, Information for People with Diabetes
World Health Organisation: Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus
NHS Choices: Diabetes