What HbA1c actually measures

Patients often bring a fasting sugar report and an HbA1c report together and ask why the two disagree. They are measuring different things.

The three-month average

A fasting sugar is a photograph of one morning. HbA1c reflects how much sugar has attached to your red blood cells over their lifespan, which is about three months. A good fasting reading on the day of the test does not move it.

Why it can mislead

Anaemia, recent blood loss, kidney disease and pregnancy can all shift HbA1c independently of your actual sugar control. That is one reason we look at both, plus your home readings, rather than any single number.

Bring your glucometer log to the consultation if you keep one. The pattern across a fortnight tells me more than either report alone.

This note is general health information and is current as at the date shown. It is not a diagnosis, not a prescription, and not a substitute for an in-person consultation. Please do not start, stop or change any medication based on it. If your symptoms are severe or sudden, call 108 or go to the nearest emergency department.