HbA1c test - diagnosing diabetes and pre-diabetes

The HbA1c test measures your average blood glucose (sugar) over 2–3 months. It is used in 2 ways: to diagnose type 2 diabetes, and to check your blood sugar levels if you have been diagnosed with type 2 diabetes.

Key points

  1. The HbA1c test can be done at any time of the day. It doesn't matter whether you have eaten or not.
  2. In New Zealand, the HbA1c test is measured in millimoles per mole (mmol/mol).
  3. If you don't have diabetes, your test results can tell whether you have type 2 diabetes, or are at risk of developing it.
  4. If you have diabetes, knowing your target range for HbA1c and having regular HbA1c tests helps you and your healthcare team monitor how well your diabetes is being controlled.
  5. The results tell you and your healthcare team whether any changes in lifestyle or medication are needed. Read more about HbA1c and monitoring type 2 diabetes. 

What does HbA1c mean?

HbA1c is what’s known as glycated haemoglobin. Haemoglobin (Hb) is the protein in your blood that carries oxygen around your body.

Glucose (a type of sugar) in your blood can stick to the haemoglobin protein. When this happens the haemoglobin is called HbA1c. The higher the glucose (sugar) levels are in your blood, the more of it gets stuck to your haemoglobin and the higher your HbA1c is.

What is the HbA1c test?

The HbA1c test is used to show your blood sugar level over the past few months. Because red blood cells only last for about 4 months (120 days), the HbA1c level only shows your blood sugar level over that time.

The amount of HbA1c used to be reported as a percentage of haemoglobin that had glucose stuck onto it, but in New Zealand HbA1c is now measured in millimoles of HbA1c per mole of haemoglobin (mmol/mol).

An HbA1c of 6% is about the same as 42 mmol/l and means the average blood sugar level is about 7 mmol/l. To compare new units with old units you can use HbA1c unit converters like this one.

How do I prepare for an HbA1c test?

The HbA1c test involves taking a sample of blood. It can be done at any time of the day. It doesn't matter whether you have eaten or not.

How is HbA1c test used for diagnosing prediabetes and diabetes?

The HbA1c test is used to diagnose pre-diabetes and type 2 diabetes.

Normal HbA1c

A result of 40 or lower is normal for people without diabetes.

Diagnosing pre-diabetes

Pre-diabetes is when the amount of sugar in your blood is higher than normal. An HbA1c level between 41-49 mmol/mol indicates pre-diabetes and means you are at much higher risk of getting type 2 diabetes and heart disease. 

Finding out you have pre-diabetes can be a chance to make changes. You may be able to stop it progressing to type 2 diabetes and increasing your risk of heart disease. Prevention is better than cure. Read more about pre-diabetes.

Diagnosing type 2 diabetes

If you have not previously been diagnosed as having diabetes, a higher HbA1c level (50 mmol/mol or greater), can indicate that you have type 2 diabetes. 

Once you have diabetes, you have it for life. But early treatment, including having a healthy lifestyle, can help to reduce damage to your eyes, kidneys, heart, feet and brain. Read more about type 2 diabetes.

 Diagnosis HbA1c level
Normal Below 40 mmol/mol
Pre-diabetes 41–49 mmol/mol
Diabetes 50 mmol/mol or above

If you have been diagnosed with type 2 diabetes, the HbA1c test is also used to monitor your diabetes and to check how well controlled your blood sugar has been over a period of time. Read more about monitoring diabetes using HbA1c. 

References

  1. Yozgatli K et al. Accumulation of advanced glycation end products is associated with macrovascular events and glycaemic control with microvascular complications in Type 2 diabetes mellitus Diabet Med. 2018 Apr 23;35(9):1242–1248.
  2. The new role of HbA1c in diagnosing type 2 diabetes BPAC, NZ, 2012
  3. Braatvedt, G D. et al. Understanding the new HbA1c units for the diagnosis of type 2 diabetes NZ Med J. 2012 Sept 23;125(1362): 70–80.
  4. Management of type 2 diabetes NZ Primary Care Handbook, 2012
  5. Stratton IM, Adler AI, Neil HA, et al. Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes: prospective observational study British Medical Journal 2000 Aug 12;321(7258): 405-12.

Reviewed by

Dr Jeremy Tuohy is an Obstetrician and Gynaecologist with a special interest in Maternal and Fetal Medicine. Jeremy has been a lecturer at the University of Otago, Clinical leader of Ultrasound and Maternal and Fetal Medicine at Capital and Coast DHB, and has practiced as a private obstetrician. He is currently completing his PhD in Obstetric Medicine at the Liggins Institute, University of Auckland.
Credits: Health Navigator Editorial Team . Reviewed By: Dr Jeremy Tuohy Last reviewed: 15 Feb 2020