HbA1c measures the number of red blood cells which have blood glucose molecules stuck to them. Too many means poor control of diabetes or a symptom of diabetes if not already diagnosed.
A non diabetic person can expect a level less than 6% (42 mmol/mol) and often below 5%.
For a diabetic person a level between 6% and 7% (53 mmol/mol) is considered to be good. Higher levels indicate poor control of diabetes. Showing HbA1c as a percentage is the old established method but it is being replaced by mmol/mol figures and this is explained below.
HbA1c is a key measure
HbA1c is a key measure for monitoring diabetic control because red blood cells (haemoglobin) don’t last in the body for more than 90 days so the figure gives a good recent history of the amount of time your blood glucose has been at high levels.
If you have had many periods of high levels of blood glucose over the last few weeks it will show in your HbA1c whereas an instantaneous blood glucose finger prick measurement won’t show that. It is the high blood sugar levels that cause the increased sticking to the red blood cells.
6-7% is good for diabetics. Since the measurement is a kind of average a figure below 6% could mean that you have had long or frequent periods of low blood glucose and that suggests you are having hypos.
The HbA1c measurement is a good guide but it cannot reveal the mishaps that you have had. It is possible to have very highly blood glucose levels at times and many hypoglycaemic episodes and still have a good HbA1c.
I once had an low HbA1c reading of 4.8% without too many hypos. Some GPs would say that result was too low because it suggests that I spent long periods at low levels and most likely had frequent hypos. At the time I was very busy with physical work and that probably helped avoid blood glucose highs.
For diagnosing diabetes measuring HbA1c is better than a normal finger prick test which measures your current blood sugar level since you might be having a good day with acceptable levels. HbA1c indicates your recent history. However, if you have undiagnosed diabetes there is a good chance your blood sugar levels will be too high all the time but the HbA1c test is more reliable.
There is now a finger prick test for HbA1c but it requires specialist equipment which is not widely available. Usually you will need to give a blood sample drawn from your arm which is sent to an analysis lab and the results take a few days.
New HbA1c mmol/mol units
HbA1c has been reported as a percentage but the new internationally established method is to use mmol/mol figures because it is more accurate especially within some cultural groups. Here is a table of how the percentage figures relate to mmol/mol.
HbA1c as a %HbA1c mmol/mol