HbA1c

HbA1c, also called glycated or glycosylated hemoglobin, measures the percentage of hemoglobin in your blood that has sugar (glucose) attached to it.

Because red blood cells live for about three months, and glucose attaches to hemoglobin in proportion to how much sugar is circulating in your blood over that period, HbA1c effectively provides an average picture of your blood sugar control over the preceding two to three months.

This makes it fundamentally different from a fasting glucose test, which only captures your blood sugar at a single moment in time and can be affected by what you ate the night before or how well you slept.

HbA1c has become the preferred test for both diagnosing diabetes and monitoring long-term blood sugar control in people already living with the condition, largely because it doesn't require fasting and gives a more stable, representative picture.