If you have diabetes or prediabetes and are at risk of developing diabetes, you may have heard your doctor discussing your ‘HbA1c’ levels – or even just your ‘A1C’ levels. But what exactly are those?
What is HbA1c?
HbA1c is a variety of haemoglobin – the component of red blood cells responsible for circulating oxygen around our bodies. Specifically, HbA1c is ‘glycated’ haemoglobin, meaning it has chemically bonded to glucose molecules.
This chemical bonding – or glycation – occurs when blood glucose reaches a particular level over an extended period of time. The principal cause of such glucose build-up is insulin resistance which can lead to diabetes.
We’ve all heard the word ‘diabetes’, but the specifics of this all too common disorder can be hazy. Diabetes affects the metabolisation of glucose, a simple sugar which serves as a fundamental source of energy for the human body. The metabolisation of glucose is controlled by a hormone called insulin. There are two circumstances in which this process can malfunction:
- If the pancreas fails to produce sufficient insulin, not enough glucose will be metabolised and it will therefore accumulate in the bloodstream.
- If a person’s body becomes increasingly resistant to insulin over time, insufficient glucose will be metabolised and it will, again, accumulate in the bloodstream.
The first situation is called Type 1 diabetes. Typically this is a lifelong disorder which first appears in childhood. It is treated by daily insulin injections.
The second situation, dubbed Type 2 diabetes, can develop if an individual eats an unhealthy diet containing high quantities of sugar and carbohydrate-rich foods for an extended period of time. This will stimulate the production of high levels of insulin which may have less and less effect over time. Type 2 diabetes is an increasingly prevalent problem in the modern western world. If doctors detect the development of insulin resistance, they diagnose the patient with so-called ‘prediabetes’.
Since a build-up of glucose in the bloodstream leads to the formation of HbA1c via glycation, blood tests which detect its presence can be used to help diagnose a patient with diabetes or prediabetes.
What are healthy HbA1c levels?
Different metrics are used to measure HBA1c levels. You may see them quoted as a percentage for example, but mmol/mol or millimoles per mol has become the international standard. A mole or mol is a chemical unit used to indicate levels of a particular substance.
Years of research and testing suggest that a normal HbA1c level is 20 – 38 mmol/mol, indicating that the person has no current risk of developing diabetes.
What are the effects of HbA1c if levels are too high or too low?
As we saw above, high levels of HbA1c rise in parallel with abnormally high blood levels of glucose.
If not properly treated, diabetes can cause serious health complications. These include:
- Nerve damage
- Impaired vision
- Impaired hearing
- Kidney disease
- Heart disease
Glycated haemoglobin levels can be affected by more than just diet. Stress, medication, illness, and lifestyle can all have an impact as well.
Unusually low levels of HbA1c are less common but when identified, they may indicate lifestyle factors or conditions that affect blood cell count. These include:
- An overly restrictive diet
- Excessive use of antibiotics and some other drugs
- Liver disease
- Recent blood loss or donation
- Genetic abnormalities
Can low or high levels of HbA1c mean you’re diabetic?
If you know you are at risk of developing type-2 diabetes then you should have a target of keeping your HbA1c below 42mmol/mol (6%). However, the American Diabetes Association categorises HbA1c levels as:
- Normal: <42 mmol/mol, or below 6%
- Prediabetes: 42-47 mmol/mol, or 6-6.4%
- Diabetes: 48 mmol/mol, or 6.5%
The NHS recommends to take a HbA1c test every 3-6 months. However, a blood test with such a result would not normally be the sole basis for a diabetes diagnosis, a GP would also consider other factors such as lifestyle, medications and any symptoms being experienced.
How to maintain healthy HbA1c levels
Diet is key to maintaining healthy HbA1c levels. Moderate your sugar and carbohydrate intake. That’s easier said than done because many food products contain high levels – especially processed foods. Eat more fresh food and learn to read food product labels carefully: not all are clearly worded and some manufacturers use jargon to disguise the true contents of their products. And finally: don’t be afraid to explore new foods – you may be surprised by how many you grow to like.
What is an HbA1c test and what does it test for?
An HbA1c blood test is designed to assess the quantities of glycated haemoglobin in your bloodstream over a period of time in order to develop as full a picture as possible of your average blood glucose levels.
It is important to be tested at least once a year if you are at risk: but it is better still to be tested every few months, especially if doctors have already established that your HbA1c is higher than it should be. This is because blood cells only circulate through our bodies for around three months before being replaced by fresh, unglycated cells. Therefore any reading can only reflect blood glucose levels for the previous twelve weeks or so.
How does the test work?
A blood sample – normally taken from the patient’s arm – is despatched for analysis in a clinical laboratory. Testing equipment will assess the amount of glycated haemoglobin present. It is not a difficult substance to detect and the amount of blood taken for the sample may be quite small. No more than a few droplets is normally required from children.
Limitations of HbA1c tests
Like most testing procedures, HbA1c tests are not flawless and cannot offer 100% accuracy. There are a number of potentially complicating factors:
- A spike in blood sugar levels in the run-up to the test can overshadow levels in the proceeding weeks, distorting the assessment. Some illnesses can cause a temporary jump in blood sugar levels.
- Pregnancy may lead to inaccurate glycated haemoglobin readings
- Anaemic patients often have abnormally low haemoglobin levels, preventing accurate test results.
Benefits of HbA1c tests
HbA1c blood tests enable accurate diagnoses of both type 1 and type 2 diabetes, as well as prediabetes. They also allow those who have already been diagnosed to proactively manage their health and avoid diabetic complications.
If you suspect that you may be at risk of developing type 2 diabetes you should certainly speak to your doctor, who will refer you for testing. But if waiting times are lengthy, why not get a head start with a home-administered HbA1c blood test? The results will lay out your personal level of risk and allow you to proactively modify your diet to reduce your chances of developing the condition.
Understanding your test results
Your HbA1c test results will be listed in the international standard measurement mmol/mol or millimoles per mol. The mole or mol is an internationally recognised chemical unit, used to measure the amount of a substance present. The mmol/mol metric is defined by the International Federation of Clinical Chemistry (IFFC).
Even slightly elevated levels of glycated haemoglobin increase your risk of developing diabetes and the associated complications. According to the National Institute for Health and Care Excellence (NICE), a patient who has already developed diabetes should be looking to maintain an HbA1c level of 48 mmol/mol or less. Meanwhile, an ideal level for a person in a state of prediabetes is 42mmol/mol or lower.
It is helpful to track your results over time and correlate these with events in your life for added context. Lifestyle changes, medication, illness and stress can all affect the results.
Medically reviewed by Sian Baker, Dip ION mBANT mCNHC – Written by Beth Giddings (BSc)