What is HbA1c?
HbA1c is a measurement that provides an indication of your average blood glucose level over the previous 10 weeks. Red blood cells contain haemoglobin (Hb), a protein that carries oxygen to our cells. Glucose attaches to Hb and “glycates” the Hb protein. Glycate Hb (as a percentage of Hb) is referred to as HbA1c. A blood test for HbA1c can be performed at any time in relation to food intake, i.e it does not require you to be fasted.
More recently, the units of HbA1c have changed from percent to mmol/mol (6.5% = 48 mmol/mol). The ideal hbA1c target varies for individual patients, but younger patients and those with a relatively recent history of diabetes (<5yrs) should aim to achieve HbA1c levels below 7% (or ideally <6.5%). Older patients and those with longer-duration diabetes may agree a target of HbA1c < 7.5%.
The Oral glucose tolerance test
This type of test is less often used nowadays. It involves measuring blood glucose levels before and after a standard 75g oral glucose drink.
Normal non-diabetics have a fasting plasma glucose value of under 6mmol/l and at 2 hours post oral glucose challenge their blood glucose level remains no higher than 7.8mmo/L. Prediabetics’ fasting value is 6-7 mmol/L and at 2-hours post drink blood glucose is between 7.9-11mmol/l. Diabetics typically have fasting values of over 7mmol/l and 2-hour peaks of over 11 mmol/L.
Fasting blood glucose test
Another measurement of blood glucose is the fasting plasma glucose (fpg) – performed after a minimum of 8 hours fasting.
FPG measurements of 5.6-6.9mmo/l reflect prediabetes. A FPG value of 7 mmo/L or more is diagnostic of diabetes.