The glycated haemoglobin or HbA1c test is used for diagnosing diabetes and monitoring the blood sugar balance.
Produced by bone marrow, the red blood cells circulate in the blood for approximately 120 days. After that, they are removed by the liver or spleen. The higher the level of glucose in the blood is, the more glucose sticks to the haemoglobin of the red cell during its lifetime.
The glycated haemoglobin level of red cells is measured using the HbA1c blood test. In Finland terms glycated haemoglobin and glycohaemoglobin are also used. It reflects the blood sugar level for a time period of approximately two months before the test. The unit of HbA1c is mmol/mol, and the reference value for a person without diabetes is 20–42 mmol/mol. However, there are individual differences when it comes to the amount of glucose sticking to the protein in red cells as well as the lifetime of red cells. That is why the values measured in different people are not directly comparable. More relevant is to monitor the way the results of the HbA1c tests of one person change or vary.
The blood test and following analysis can be conducted in a laboratory or as a quick fingertip test at an appointment. There are different HbA1c test methods. Conducted by a different lab or using a different method, the test results may be slightly different.
Fasting is not required for the HbA1c test.
Previously, HbA1c results were given as a percentage. Now, the result is given as mmol/mol. If the units need to be converted into a percentage, you can use the following correlation as a rule of thumb.
HbA1c mmol/mol
HbA1c %
40
5,8
45
6,3
50
6,7
55
7,2
60
7,6
65
8,1
70
8,6
75
9,0
80
9,5
The HbA1c test can be used for a type 2 diabetes diagnosis. Without diabetes, the glycated haemoglobin value is 20–42 mmol/mol. A value of 42–47.9 mmol/l corresponds with pre-diabetes. The diabetes diagnosis limit is 48 mmol/mol.
The HbA1c value is not used for the diagnosis of type 1 diabetes or gestational diabetes because it may be erroneously low, especially with regard to a condition that occurs rapidly. But even in these cases, the HbA1c test will show if the blood sugar level has been high for an extended period of time.
The higher the blood sugar level is, the more glucose is attached to the haemoglobin in red blood cells as well as other proteins in tissues. This is why the HbA1c tests can also be used to analyse the long-term glucose load of the body and the risk of possible complications related to high blood sugar.
The HbA1c test is normally carried out 2 to 4 times per year, depending on the individual in question. The target is individually set. The target value may be dependent on factors such as the person’s age, ability to function, low blood sugar sensitivity and individual situation of diabetes management.
The recommended target value according to treatment guidelines is below 53 mmol/mol without recurring too low blood sugars. It corresponds to an average blood sugar level of 8.5 mmol/l.
Sometimes, it may appear that the HbA1c result and your own blood sugar tests are in conflict. Usually, the reason for the disparity is that blood sugar is normally checked before meals, and high levels after meals or at night may go undetected.
The HbA1c value may also be affected by factors which shorten or extend the lifetime of red cells. If the lifetime of red cells is shorter than normal or red cell production has accelerated, the HbA1c value is lower compared to a blood sugar test done at home. For example, various anaemias and their treatments as well as acute kidney failure have an effect on the HbA1c result.
