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HbA1c testing

The HbA1c test measures your average blood glucose over the previous 8 to 12 weeks and gives an indication of your longer-term blood glucose control. It is used as a screening test to identify diabetes and regular monitoring tool if you have been diagnosed with diabetes.

How useful is the test?

HbA1c reflects the average plasma glucose (sugar in your bloodstream) over the previous 8 to 12 weeks and measures how much glucose has become stuck onto your red blood cells.(1)

  • It can be performed at any time of the day and does not require any special preparation such as fasting.
  • In recent years, the HbA1c test has become the preferred test for screening and diagnosis of diabetes.

HbA1c levels dial diagramIn 2011, the HbA1c test in New Zealand was updated to measure in millimoles per mole (mmol/mol) to align with a shift internationally (2). Prior to this, it used to be measured as a percentage (%) and you may still hear people refer to these units at times. The images below show the new and old units. 

HbA1c chart and units HbA1c bands

Learning what your target range for HbA1c is very important. Having regular HbA1c tests helps both you and your healthcare team monitor how well your diabetes is controlled and whether any changes in lifestyle or medication are needed. 

Diagnosing prediabetes and diabetes

As a general guide, HbA1c levels of: 

  • Less than or equal to 40 mmol/mol is normal.
  • 41 to 49 mmol/mol is prediabetes or 'impaired fasting glucose'.
  • 50 mmol/mol and above suggests diabetes (if symptomatic. If no symptoms of diabetes, two tests on separate occasions are needed). (3) 

Read more about prediabetes, type 1 diabetes and type 2 diabetes.

What are healthy HbA1c levels for people with diabetes?

An ideal range or target HbA1c level will vary from person to person and depends on age, type of diabetes and other health conditions or stages (such as pregnancy). Ask your doctor or nurse what your target HbA1c is. 

The following ranges provide a general guide: 

  • Less than or equal to 53 mmol/mol is a very healthy HbA1c level.
  • Between 54 mmol/mol and 63 mmol/mol is a fair HbA1c level and needs work to improve.
  • Between 64 mmol/mol and 86 mmol/mol indicates your blood glucose levels are much too high.
  • Above 86 mmol/mol indicates your blood glucose levels are extremely high and urgent action is required. 
If you are taking insulin and your HbA1c level is too low, you are at higher risk of having low blood glucose levels ('hypos' or hypoglycaemia). In this case, talk with your doctor/nurse about whether you need to reduce your insulin dose or frequency. 

Why is tight diabetes control so important?

A number of studies have shown the many benefits of reducing a high HbA1c level. In these studies, the equivalent of an 11 unit decrease in HbA1c eg. from 86 to 75 mmol/mol or 75 to 64 mmol/mol leads to: 

  • a 16% decrease in risk of heart failure
  • a 14% decrease in risk of fatal or non-fatal myocardial infarction (heart attack)
  • a 12% decrease in risk of fatal or non-fatal stroke
  • a 21% decrease in risk of diabetes-related death
  • a 14% decrease in risk of death from all causes
  • a 43% decrease in risk of amputation
  • a 37% decrease in risk of small blood vessel disease (eg, retinal blood vessel disease causing vision loss). (4)

The sooner you take control of your health and do all you can to get your blood glucose and HbA1c levels down into the optimal range, the better. Learn all you can about balancing food, activity levels and medications.

If you are overweight (which most people with type 2 diabetes are) then losing some weight can often be the best thing you can do. In some cases, people have managed to reverse their diabetes by getting back to a healthy body weight and adopting healthier eating and activity patterns. 

Work with your doctor/nurse and diabetes team to learn what approach is best for you and regain good diabetes control.

If you are on insulin or have high HbA1c levels, then also ask about self-monitoring of your blood glucose levels. 

NOTE: if viewing American websites, watch out for different units. In the USA, blood glucose is measured as mg/dL. Visit Diabetes UK to convert blood sugar/glucose from mmol/L (UK standard) to mg/dL (US standard) and vice versa.

References

  1. World Health Organization. 2011. Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus.
  2. Braatvedt, G D. et al. Understanding the new HbA1c units for the diagnosis of type 2 diabetes. NZMJ Sept 2012. Vol 125 No 1362: 70-80
  3. Management of type 2 diabetes. NZ Primary Care Handbook 2012
  4. Stratton IM, Adler AI, Neil HA, et al. Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes (UKDPS 35): prospective observational study. British Medical Journal 2000; 321 (7258): 405-12


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Source: Health Navigator