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Understanding HbA1c & blood glucose

Understanding HbA1c & blood glucose

What is it? How is it measured? How does it affect me?

Knowing your HbA1c is very useful when living with diabetes. It measures your average blood glucose level over the last 8-12 weeks. 

Your HbA1c level is linked to your risk of developing complications from type 2 diabetes. A high HbA1c is associated with a high risk of damage to blood vessels (arteries) and this can increase the risk of nerve injury, sight problems, kidney disease, heart attacks or strokes. So taking steps to lower your HbA1c to your target level is important to stay healthy.

HbA1c can be measured with 2 different units - in mmol/mol or as a percentage.

For someone who is well and has recently been diagnosed with type 2 diabetes, the aim of treatment would be to get your HbA1c below 48 mmol/mol (6.5%). People with more complex medical needs might be advised to aim for an HbA1c of 58 mmol (7.5%). Your individual target will depend on a number of things like age, how long you have had diabetes, how many blood glucose lowering medicines you need and any other medical conditions you might have.

The advantage of HbA1c is that it changes slowly and it is not affected by what you have just eaten. So you do not need to fast before you have your blood test.

The disadvantage of HbA1c is that it changes slowly. So any change you make to your diet, exercise or medication will take 6 weeks to show its effect, and the full impact of doing something different might not be visible for 2-3 months. Testing HbA1c is also not suitable for people with certain medical problems - these are described in the extra information section later in this article. Generally you should get your HbA1c tested every 6-12 months.

So how does your HbA1c level link with your actual blood glucose readings? It is slightly different for different people, but you can use the table below as a rough guide. An ideal fasting blood glucose level is around 5 to 7 mmol/l.

Extra information

What exactly does an HbA1c test measure?

The HbA1c blood test measures how much glucose (sugar) is part of your red blood cells. The higher your blood glucose levels, the more glucose gets attached to the haemoglobin inside these blood cells.

This is a slow process that happens over days or weeks. That is why it doesn’t change straight after eating or drinking something - unlike a finger prick test for blood glucose which responds very quickly to food or drink.

Who can’t have an HbA1c test done?

HbA1c is a very useful test for most people with type 2 diabetes, but it is not appropriate for everyone.

Some people have different forms of haemoglobin in their blood - like HbS, HbC or HbE. People with these haemoglobin variants will need to get a different test done to measure something called fructosamine. In the UK, the hospital will often do this automatically for you when they notice a haemoglobin variant.

Testing HbA1c is also not suitable for people who are pregnant, anaemic or have severe kidney or liver problems.

How can I lower my HbA1c?

Lowering your blood glucose levels will lower your HbA1c. You can achieve this by eating less sugar or carbohydrates, increasing your physical activity levels and taking your medication regularly.

In terms of what you eat and drink, you should try to:

  • Avoid sugary food
  • Avoid sugary drinks, fruit juices and smoothies
  • Eat smaller portions of starchy food like potatoes, bread, pasta, rice, noodles or yams
  • Have 1 piece of whole fruit or a handful of nuts when you snack
  • Eat more vegetables (potatoes and other starchy vegetables should be avoided)

All physical activity is helpful in lower blood glucose levels - this could be walking, running, cycling, swimming or an exercise routine at home. A good workout can continue to lower your blood glucose levels for up to 3 days.

There are many types of medicines that can be used to lower blood glucose levels. Examples of these are metformin, gliclazide, -gliptins, -glutides, -flozins and insulins.

Posted by Dr Kingshuk Pal
The advice we are providing is as accurate and as comprehensive as possible, but it is only general advice and should not be used as a substitute for the individual advice you might receive from consulting your qualified medical practitioner. Please ensure you consult a qualified medical professional before making any changes to your healthcare.