glycated haemoglobin · A1c · average blood sugar
HbA1c: what your result means
HbA1c is an average of your blood sugar over the past two to three months — which is exactly why it cannot be improved by fasting the night before.
What it measures
Glucose sticks to the haemoglobin inside red blood cells and stays stuck for the life of the cell. HbA1c measures what fraction is coated, so it reflects your average glucose over roughly the previous eight to twelve weeks, weighted towards the most recent ones.
Why it gets tested
To diagnose and monitor type 2 diabetes and prediabetes, and to see how well treatment is working. It is used for screening in people with risk factors — family history, higher weight, high blood pressure, previous gestational diabetes — because it needs no fasting and only one sample.
Typical ranges
In most laboratories, below 5.7% (39 mmol/mol) is normal, 5.7–6.4% (39–47) is prediabetes, and 6.5% (48) or above on two occasions supports a diagnosis of diabetes. Treatment targets are individual: often around 7% (53), but deliberately higher in older people or where low blood sugar is a risk.
Compare against the range printed on your own report, not this one. Laboratories differ, and yours is the one your doctor is reading.
What a high result can mean
A raised HbA1c means average glucose has been high — usually type 2 diabetes or prediabetes, but steroid treatment, some antipsychotics, Cushing's syndrome and pancreatic disease do it too. A result just over a threshold is normally repeated before anything is concluded from it.
What a low result can mean
A low HbA1c is rarely a glucose problem. More often red blood cells are not living long enough to accumulate glucose: haemolytic anaemia, recent bleeding or transfusion, advanced kidney or liver disease, pregnancy and some haemoglobin variants all lower it — and in those situations HbA1c stops being a reliable measure of average glucose at all.
What moves it
Anything that changes red cell lifespan. Iron deficiency can raise it; haemolysis, bleeding and pregnancy lower it. Haemoglobin variants — common in people of African, Mediterranean and South-East Asian ancestry — can make some assays read wrongly in either direction, and kidney disease affects it both ways.
What usually happens next
A prediabetes result usually leads to a repeat, a conversation about weight, food and activity, sometimes metformin, and a check of blood pressure and lipids, because those travel together. A diabetic-range result leads to confirmation, then treatment and the checks that go with it — kidney function, urine protein, eyes and feet.
Common questions
Do I need to fast for an HbA1c?
No, and that is one of its advantages. It reflects months of glucose, so what you ate that morning makes no difference. Fasting glucose and the glucose tolerance test do require fasting; HbA1c does not.
How quickly can I change it?
Meaningfully in about three months, which is why it is usually rechecked at that interval. The most recent weeks count for more than earlier ones, but a single good week will not move it much.