D. 15 – Explanation

Glycosylated haemoglobin
Glycosylated haemoglobin (HbA1c) is the most widely used measure of long-term glycaemic control
in diabetes mellitus. HbA1c is produced by the glycosylation of haemoglobin at a rate proportional to
the glucose concentration. The level of HbA1c therefore is dependant on

• red blood cell lifespan
• average blood glucose concentration

HbA1c is generally thought to reflect the blood glucose over the previous ‘2-3 months’ although there
is some evidence it is weighed more strongly to glucose levels of the past 2-4 weeks
The relationship between HbA1c and average blood glucose is complex but has been studied by the
Diabetes Control and Complications Trial (DCCT). A new internationally standardised method for
reporting HbA1c has been developed by the International Federation of Clinical Chemistry (IFCC).
This will report HbA1c in mmol per mol of haemoglobin without glucose attached.

From the above we can see that average plasma glucose = (2 * HbA1c) – 4.5