What is HbA1c?

Glucose attaches in proportion to how much of it is around, so HbA1c is a record of exposure rather than of the moment blood was drawn. Sustained contact with glucose is what damages the small blood vessels of the eyes, kidneys and nerves over years.

Fasting Glucose measures the sugar at one moment, and Fasting Insulin and HOMA-IR measure the insulin holding that sugar down. Haemoglobin and MCV, the average red cell size, describe the cells themselves rather than the glucose attached to them, and how long those cells last shapes what HbA1c records.

Carbohydrate intake and the body's sensitivity to insulin shape HbA1c over months. Anaemia works differently, shortening red cell life so there is less time for glucose to accumulate. Inherited haemoglobin variants change the protein the test measures, and pregnancy and kidney or liver disease change how long red cells last, so each can move HbA1c when glucose has not.

HbA1c cannot move faster than red blood cells are replaced. They survive around 120 days, so the measure reflects roughly the previous two to three months, and a single unusual week does not shift it. Testing about every four months means each measurement covers most of the stretch since the last one, so the year is read in consecutive spans rather than from a single point. This is Do Health's monitoring schedule, not a general recommendation for everyone.