HbA1c

Most UK laboratories print 20 to 41 mmol/mol for the general population, and show 42 to 47 and 48 and above as separate bands. The figure is unreliable in the general population where red cells live for a shorter or longer time than usual, for example after blood loss, in some anaemias and with some inherited haemoglobin variants.

HbA1c is haemoglobin, the protein in red blood cells, with glucose attached to it. The more glucose there has been in the blood, the more haemoglobin becomes coated. Because red cells live for about three months, the figure gives an average of blood sugar over that time rather than a snapshot of one moment. In the UK it is reported in mmol/mol; the older percentage is the same test in different units.

It is the main test doctors use when looking at how the body has handled sugar over the previous two to three months, both in routine checks and in following people who have diabetes.

• Diabetes and pre-diabetes
• Steroid medicines
• Iron or vitamin B12 deficiency, because red cells live longer
• Kidney disease
• Older age, a little, in the general population

• Better sugar control with diet, exercise, weight loss and diabetes medicines
• Anything that shortens the life of red cells, such as blood loss, haemolysis or a recent transfusion
• Pregnancy, in the second and third trimesters
• Some inherited haemoglobin variants, depending on the laboratory method
• Treatment of iron or B12 deficiency, for a few weeks

• No fasting is needed and a recent meal does not affect it
• Anything that changes how long red cells live changes the figure without any change in blood sugar
• Different laboratory methods handle haemoglobin variants differently

No fasting needed and the time of day does not matter. It reflects the previous two to three months, so it is usually repeated no more often than every three months. Read the trend rather than a single value.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.