What Your HbA1c Number Actually Means

HbA1c is the number most people end up watching, and it is worth understanding what it actually measures.

Glucose in your blood sticks to haemoglobin, the protein inside your red blood cells. Those cells live for around three months. So measuring how much glucose is stuck to them gives an estimate of your average blood sugar over that period, reported as a percentage.

This is its strength and its weakness. It smooths out a single bad day, which a fingerstick reading cannot do — and it also hides the pattern. Two people with the same HbA1c can have very different days, one steady and one swinging between highs and lows.

For diagnosis, 5.7% to 6.4% is the prediabetes range and 6.5% or above indicates diabetes. Once you have diabetes, the commonly used target is below 7%, though your own target may be set higher or lower depending on your age, how long you have had diabetes, other health conditions, and whether you have been getting low blood sugar.

It is usually checked every three to six months, alongside your day-to-day target ranges. Do not read too much into a small change — a shift of a tenth or two is within normal variation, and the direction over a year matters far more than any single reading.