HbA1c Test – Explained & Why You Should Pay Attention To It

Every 6 months to a year you should be invited to visit your GP for your diabetes review. Here the practice nurse or your doctor should perform your basic diabetes MOT.

The 15 health check essentials shall be examined in another post. What I want to discuss here is the HbA1c test and what exactly it means to your diabetes care.

The Test

The HbA1c test is a simple blood test where the average blood glucose level for the previous 3 months is examined. This can provide valuable insights into how well your blood glucose levels have been managed.

We are able to do this because glucose sticks to the haemoglobin within red blood cells. HbA1c literally means glycated haemoglobin (glucose on haemoglobin). Even individuals without diabetes will see some glucose sticking to their red blood cells but typically those suffering with diabetes will have greater levels.

Red blood cells have a 3 month life span within the body before they are cleared in the spleen. Therefore, by sampling the red blood cells, we can analyse the amount of glucose stuck to them. This is a direct indication of how well your blood glucose levels have been controlled.

There is no point in repeating this test any more regularly than 3 months apart because of the prolonged life span of the red blood cells. Essentially, you would be looking at the same or similar data.

It is for this reason, GP’s and surgeries only invite you between every 6 months to a year.

The Numbers

Those of you who have had diabetes for quite some time will remember the HbA1c was previously reported in percentages. This has changed in recent years because it was felt the percentages often in single figures were too similar the to numbers seen when testing your blood glucose levels day to day. This was found to be confusing for patients and thus the change was made.

We now measure the HbA1c in mmol/mol. The gold standard for good control is a HbA1c of 48-58mmol/mol. Currently we diagnose type 2 diabetes when an HbA1c reaches 48mmol/mol. 48mmol/mol corresponds to 6.5% in the old method.

The reason for the 48-58mmol/mol target is because research has demonstrated control better than this produces no significant benefit in terms of long term risk reduction. In those patients taking insulin, often control below 48mmol/mol results in frequent hypoglycaemic episodes which drastically increases their risk of coming to harm without the added benefit of reducing their risk complication rate from diabetes.

However, once the HbA1c begins to rise above 58mmol/mol the picture begins to change. At this point, the risk of developing retinopathy (eyes), neuropathy (nerves), nephropathy (kidneys), circulatory problems,  increased cholesterol, reduced gastric emptying rates and many more complications begins to drastically increase.

This is detailed in the graph below:


The relative risk along the left hand side refers to 1 being normal risk. As you can see, once the HbA1c increases above around 7-7.5% (58mmol/mol) the lines start an upward trend. Each number along the left hand side refers to how many times more likely someone is to develop a complication which corresponds to the HbA1c along the horizontal axis at the bottom. For example, someone with an HbA1c of 10% (86mmol/mol) is around 8 times more likely to develop diabetic retinopathy than someone at 7%.

As you begin to improve your control your relative risk will decrease. If you already suffer with complications you can reduce the progression of such complications but in some instances a degree of damage may already be done. This is why it is a good idea to try to control this early in your diagnosis.

In fact, those who gain good control over their diabetes early in their diagnosis, can reduce their risk long term. In other words, controlling the disease early has knock on beneficial effects. If you are not newly diagnosed , do not worry, you can always improve your control and thus reduce your risk of developing or further developing complications.

HbA1c Below 48mmol/mol

You may remember I mentioned type 2 diabetes is officially diagnosed at an HbA1c of 48mmol/mol with pre-diabetes being diagnosed at 42mmol/mol.

Therefore, it seems logical to think if your HbA1c drops below these values you no longer suffer with diabetes. There is currently a great body of work looking into this using very low calorie diets to help push type 2 diabetes into remission. The preliminary work looks promising but is not conclusive and is yet to be published.

Those newly diagnosed (within 2 years) have the best chance of achieving remission. but before you get excited there are some things we need to cover.

First, your type of diabetes will be a big factor. Those suffering with type 1 produce no insulin of their own. Therefore, the disease has not manifested in the same way as type 2 diabetes. In type 1 diabetes, the body’s own immune system destroys the cells of the pancreas which produce insulin. Therefore,  pushing your HbA1c level below 48mmol/mol does not cure your diabetes. In line with the graphs displayed above, reducing your HbA1c below 48mmol/mol does not produce significant benefits compared to an HbA1c of 48-58mmol/mol and increases the risk of persistent hypoglycaemic episodes. That said, if you are able to achieve levels below 48mmol/mol without hypoglycaemic episodes, it will translate into good control. However, your diabetes will not be remission.

Type 2 diabetes on the other hand, is primarily the result of lifestyle and specifically carrying excess weight. Therefore, this disease is ideally placed for lifestyle interventions to help manage the disease.

With dietary changes and regular exercise alongside weight reduction, it is possible to push the type 2 diabetes into remission or at least significantly improve your control.

Two scenarios where this may not be the case is if you completely cut out your carbohydrates without losing weight and/or improve your fitness and if you are taking various medications to help reduce your HbA1c.

Lets start with diet. If cutting out carbohydrates and therefore your glucose intake your HbA1c will be towards the lower end and possibly below the 48mmol/mol diagnostic level. What you haven’t necessarily done though is address the underlying cause of the disease which is the insulin resistance and possibly lack of fitness. In essence, you have plastered over the cracks. If you were to ear carbohydrates your blood glucose levels would likely spike above normal levels. Therefore, for true remission you would need to address the underlying cause by improving your fitness and reducing your weight.

Alternatively, your HbA1c level may drop below 48mmol/mol but you may remain on multiple therapies e.g. metformin, sitagliptin, empgliflozin and insulin. In this instance your diabetes is very well controlled but take away those medications and we may see a very different picture.

Therefore, it is always good to make lifestyle changes and assess the effect of these on your HbA1c. You may find over time your GP becomes satisfied enough to start reducing the medications but this may take time.

You can therefore make a huge difference to your diabetes control through diet and lifestyle changes and in some instances this may even result in your diabetes entering remission.

Pro’s and Cons of HbA1c

The HbA1c is a great way of assessing the overall picture of your diabetes control over a significant period of time. There is no way of cheating or manipulating this test like you can with your day to day blood glucose tests. It provides a relatively accurate picture of how your control has been over the previous 3 months. This is particularly true when seeing HbA1c’s at the upper end of the spectrum.

However, there are cons to the test. One drawback is that it is an average. Therefore, you could have blood glucose levels that swing between really high followed by severe hypo’s but the average may imply good control.

Another drawback is because it is a blood test looking at the red blood cell count, those who are anaemic may find their results are slightly skewed. This is because they have less haemoglobin within the red blood cell which in turn can give incorrect results.

On the whole, the HbA1c is a good measure of your diabetes control and I would urge you to regularly attend your appointment and know your level.



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