The HbA1c Test Explained

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Every 6 to 12 months you should be invited to visit your GP for your diabetes review and HbA1c test.. Here the practice nurse or your doctor should perform your basic diabetes MOT. You will be examined for the 15 health check essentials which we have blogged about previously here. One of these checks is the HbA1c test which measures a 3 month average of your glucose levels. This helps you and your diabetes team put your glucose control into perspective and devise a plan going forwards.

The HbA1c 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 circulating in the blood. HbA1c literally means glycated haemoglobin (glucose on haemoglobin). Even individuals without diabetes will see some glucose sticking to their red blood cells. However, 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 every 3 months because of the prolonged life span of the red blood cells. Essentially, you would be looking at the same or similar data. It is one of the 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.  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. It is also now consistent with Europe and how they measurer their HbA1c. We now measure the HbA1c in mmol/mol. The gold standard for good control is a HbA1c of 48-59mmol/mol (6.5-7.5%). Currently we diagnose type 2 diabetes when an HbA1c reaches 48mmol/mol. 48mmol/mol corresponds to 6.5% in the old method. Often the temptation is to drive the HbA1c as low as possible. Research has yet to demonstrate a HbA1c any lower than 48mmol/mol produces any significant reductions to long term complications risk. In those patients taking insulin, often control below 48mmol/mol results in frequent hypoglycaemic episodes.  This drastically increases their risk of coming to harm without the added benefit of reducing their risk of complications from diabetes. We will discuss this in more detail shortly. Once the HbA1c begins to rise above 59mmol/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:

Relative Risk of long term complications with rising HbA1c

HbA1c 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% (59mmol/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. This 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% (55mmol/mol. As you begin to improve your control your relative risk will decrease. If you already suffer with complications you can still 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.

HbA1c below 48mmol/mol in Type 1 diabetes

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 come about 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 48-59mmol/mol and increases the risk of persistent hypoglycaemic episodes (hypo’s). Hypo’s can be life threatening if severe enough but usually they just make you feel a bit jittery until you treat them with some carbohydrate. What is less appreciated is the long term effects of persistent hypo’s. Each hypoglycaemic episode gives a little kick to the brain and cardiovascular system and can lead to its own complications long term. These include dementia and/or heart attacks. Therefore, you will be encouraged to avoid hypos. That said, if you are able to achieve levels below 48mmol/mol without hypoglycaemic episodes, it will translate into very good control. However, your diabetes will not be remission.

HbA1c below 48mmol/mol in type 2 diabetes

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. True remission is when you are taking no glucose lowering therapy and have a HbA1c below 42mmol/mol. If you continue on medications but have a HbA1c below 48mmol/L you are very well controlled. This is assuming you are not taking any medications that can push your glucose too low such as insulin and sulphonylureas. You might also be able to achieve remission figures by cutting out most of the carbohydrates in your diet. This isn’t particularly advised because it means cutting out a lot of healthy foods. Including fruit and vegetables. A low carbohydrate diet might be suitable however. We have blogged on this previously here. However, true remission is not achieved until you can eat carbohydrates without experiencing hyperglycaemia. This is usually achieved through increasing your exercise, changing your diet and losing weight. 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

Pro’s

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.

Cons

However, there are cons to the test. One drawback is that it is an average. Therefore, it is susceptible to being skewed by high and low glucose levels. Two people may have the same HbA1c despite one person swinging between 20mmol/l and 3mmol/l and the second person being consistently 5-8mmol/l. Another drawback is for 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.

Summary

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. It will always be part of your 15 essential health checks and should be measured at least yearly. It will change throughout your diabetes life and try not to be discouraged if it is higher than you would like. Diabetes is a process and sometimes takes time to figure it out.

Need more help

If you need more support we offer a range of 1:1 consultancy services and online programmes focused on helping you improve your glucose control and health for the long term. These include our type 2 diabetes recovery programme, type 1 glucose stability programme and winning weight loss programme. Go to the pages using the links above or in the headers or get in touch if you have questions.

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