What it measures
Sugar in the blood gradually attaches to the haemoglobin in red blood cells. HbA1c measures that share of sugared haemoglobin: it reflects the average blood sugar of the last two to three months, not this morning's.
How it is taken
One lavender-cap tube is enough, with no fasting. It can be given as a percentage or in mmol/mol: your patient space lets you switch from one unit to the other.
Why follow it
The doctor looks above all at how one HbA1c compares with the next. Your patient space shows your successive values on the reference range; it is your doctor who draws the conclusions for you.