HbA1c explained: your three-month sugar average

A fasting glucose tells you what your blood sugar was at the moment the needle went in. HbA1c tells you something more useful for most people: roughly where your sugar has been sitting, on average, over the last two to three months. It is the single most important number for spotting diabetes and for checking how well it is controlled.

How the test works

Haemoglobin is the protein in red blood cells that carries oxygen. Sugar in the blood sticks to it slowly and permanently, a bit like a stain. The higher your sugar runs, the more haemoglobin gets coated. HbA1c measures the share of haemoglobin that carries this sugar coating.

Red blood cells live for about three months, so the result reflects that window. The most recent few weeks count the most. This is why one indulgent weekend barely moves HbA1c, while months of high sugar push it steadily up. It also means you do not need to fast for this particular test, although other markers on the Diabetes Check do need a fast.

Reading your result

Labs in South Africa usually print HbA1c as a percentage. Some also show it in mmol/mol, a newer international unit. An HbA1c of 6.5% is the same as 48 mmol/mol, and 6.0% is about 42 mmol/mol. LifePrint follows the 2017 guideline of the Society for Endocrinology, Metabolism and Diabetes of South Africa (SEMDSA):

• Below 6.0%: not in the at-risk range.
• 6.0 to 6.4%: at risk. This is LifePrint's grey zone for HbA1c, and it calls for a fasting glucose or a glucose tolerance test to look more closely.
• 6.5% or more: in the diabetes range. SEMDSA asks for this to be confirmed with a repeat test, unless you have clear symptoms or a very high glucose at the same time.

Why LifePrint does not use the 5.7% cut-off

If you have read American health websites, you may have seen prediabetes defined as an HbA1c from 5.7%. That cut-off comes from the American Diabetes Association (ADA). SEMDSA chose not to adopt it and uses 6.0% as the start of the at-risk range, in line with the international expert group that first proposed HbA1c for diagnosis.

The reasoning is practical. A lower cut-off labels far more people as having a condition, many of whom would never go on to develop diabetes. HbA1c is also less exact in populations where anaemia and inherited haemoglobin variants are common, which is the case in South Africa. Starting at 6.0% focuses attention on the people at highest risk, without turning a large share of healthy adults into patients. LifePrint applies the SEMDSA ranges so your result is judged against the guideline your South African doctor will use.

When HbA1c can mislead

Because HbA1c depends on red blood cells, anything that changes how long they live or how much haemoglobin you have can shift the number without any change in your sugar. Common examples include:

• Iron deficiency, which can push HbA1c falsely up.
• Recent blood loss, a blood transfusion or a condition that breaks down red cells faster, which can push it falsely down.
• Inherited haemoglobin variants, such as sickle cell trait, which can affect some lab methods.
• Advanced kidney disease and pregnancy, where HbA1c is harder to interpret.

This is one reason the Diabetes Check measures fasting glucose alongside HbA1c. When the two agree, you can be confident in the picture. When they disagree, it is a signal to look for one of these explanations before drawing a conclusion.

How often to test

If your HbA1c is well below 6.0% and you have no strong risk factors, testing every few years is reasonable. In the at-risk range, a yearly check lets you see whether changes to eating, activity and weight are working. People already living with diabetes are usually tested every three to six months, as their doctor advises. Because HbA1c reflects about three months, testing more often than that rarely adds much.

What happens after a flagged result

Your LifePrint report explains where your result sits and how urgently to follow up. A result in the grey zone is routine, not an emergency. A result in the diabetes range means you should see a registered healthcare practitioner soon to confirm it and plan the next steps. Your report is health information, not a diagnosis, and a doctor is the right person to make that call with you.