HbA1c Test

The HbA1c test shows how well your diabetes has been controlled over the last 2-3 months. Even if your blood glucose has occasionally been very high or low, HbA1c will give an estimate of the average level of glucose in your blood over that time-period. The result can help you and your healthcare professional 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) recommends that 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. Some of these include:  

• All symptomatic children and young people  
• Pregnancy - current or recent (< 2 months) 
• Suspected Type 1 diabetes no matter what age 
• Patients with symptoms of diabetes for less than two months. 
• Patients at high risk of diabetes who are acutely ill (such patients must be retested once the acute episode has resolved) 
• Patients taking medication that may cause rapid glucose rise e.g. corticosteroids, antipsychotics 
• Haemoglobinopathy (HbS, HbC etc), i.e. an uncommon type of haemoglobin 
• Anaemia (Hb <105 g/L) 
• Recent blood transfusion 

An oral glucose tolerance test should be used to diagnosis diabetes, if HbA1c cannot be used. 

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, as mentioned above, in which HbA1c cannot be used to diagnose diabetes. 

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. There is a high risk of progression to type 2 diabetes. 
• HbA1c of 48 mmol/mol or over: indicative of diabetes. If patient is symptomatic, diagnosis is confirmed.  If asymptomatic, repeat testing within 4 weeks is required for confirmation. 

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. The HbA1c test is not used for diagnosing diabetes during pregnancy or for diagnosing type 1 diabetes. 

For people with type 1 diabetes, the National Institute for Health and Care Excellence (NICE) recommends that HbA1c be measured every three to six months. Whereas, for adults with type 2 diabetes, NICE recommends HbA1c be measured every three to six months (tailored to individual needs), until the HbA1c is stable on unchanging therapy. Subsequently, once the HbA1c level and blood glucose-lowering therapy are stable, HbA1c should be measured every 6 months.