Complications of Diabetes

HbA1c (Haemoglobin A1c)

What is Haemoglobin A1c (HbA1c)?

Haemoglobin is the substance in the blood that carries oxygen within red blood cells. Over time, glucose binds very slowly to haemoglobin and results in glycated haemoglobin. This glycated haemoglobin can be measured and provides an estimate of average blood sugar levels. In people who do not have diabetes levels between 4 and 6% are observed.

DCA2000 HbA1c analyser

DCA2000 HbA1c Analyser  used at West Suffolk Diabetes centre

The life span of a red blood cell is 90 to 120 days in circulation. This is why the HbA1c measurement tells us what your blood sugars have been doing over the past three months.

What is the importance of measuring HbA1c?

The HbA1c is the best single measurement available to clinicians to assess your overall diabetes control and the risk of complications of diabetes.

The Diabetes Control and Complications Study, a landmark study of people with Type 1 diabetes conducted in the early 1990s, showed that the risk of devlopment and progression of complications of diabetes increased with HbA1c.

Can you diagnose diabetes using HbA1c?

No. The HbA1c has no value whatsoever in making a diagnosis of diabetes. However, once the condition has been diagnosed using blood sugar measurements, HbA1c is useful for monitoring control.

The risk of complications is not linear!

With increasing haemoglobin A1c the risk of complications of diabetes tends to rise disproportionately.


As you can see from the graph the risk of complications increases substantially with a small increase in HbA1c of 1%.

How often should I have my HbA1c checked?

We recommend you have an HbA1c at least twice a year. For those who are consistently well controlled once a year should suffice.

What is the target HbA1c?

Targets in many ways depend on the individual patient as there are many variable factors which would influence your ability to achieve a given target. In general an Hba1c of 6.5% represents ‘good’ control, a level of 7% ‘satisfactory’ or ‘fair’ and a level greater than 7.5% is indicative of poor control. It is worth emphasizing that it may not be appropriate to aim for a level of 6.5% in someone who is elderly or prone to recurrent hypoglycaemia.

Why do I find it impossible to hit the target HbA1c?

There are many reasons you may struggle to achieve good control. Insulin resistance is a common cause with spiralling insulin doses resulting in weight gain and further limitation of exercise resulting in worse control. Losing weight if you are obese will probably help more than increasing your dose of insulin.

Remember oral hypoglycaemic drugs and insulin are only a small part of blood glucose control. By far the more important aspect of achieving good control of blood sugar is diet and exercise.


Dr Nishan Wijenaike MD, FRCP
Consultant Diabetologist
West Suffolk Hospital NHS Trust
July 2005