What is HbA1c and how is it formed?
Hemoglobin is the red blood pigment and enables the transport of oxygen and carbon dioxide in the body. There are different types of hemoglobin, with normal adult hemoglobin being called HbA.
However, a patient with diabetes has an elevated blood glucose level for a longer period of time. As a result, the bond between sugar and hemoglobin becomes strong and indissoluble. It remains in place until the red blood cells are broken down at the end of their life. This is the case after about three months. The HbA1c value therefore provides information on how high the sugar concentration was on average in the patient’s blood within the last few weeks.
HbA1c: units of measurement
However, a new method of the International Federation of Clinical Chemistry (IFCC) is now regarded as an international reference point: it gives the value in millimoles per mole of hemoglobin (mmol/mol Hb). The units of measurement can be converted into each other using a formula:
Hemoglobin A1c (IFCC) in mmol/mol Hb = (%HbA1c -2.15) : 0.0915
HbA1c: Reference values
HbA1c: Table with normal and limit values.
There are two different assessment guidelines here:
According to the St. Vincent Declaration, HbA1c values are assessed as follows:
|
Percentage value HbA1c |
Assessment |
|
< 6,5 % |
Diabetes well controlled |
|
6,5 – 7,5 % |
Diabetes moderately adjusted |
|
> 7,5 % |
Diabetes poorly adjusted |
According to the recommendation of the European Expert Commission, on the other hand, the values are assessed as follows:
|
Percentage value HbA1c |
Assessment |
|
< 6 % |
no diabetic condition |
|
6 – 7 % |
|
|
7 – 8% |
Diabetes excellent adjusted |
|
8 – 9 % |
Diabetes well adjusted |
|
9 – 10 % |
Diabetes satisfactorily adjusted |
|
> 10 % |
Diabetes poorly adjusted |
In children and adolescents with diabetes, the HbA1c should be below 7.5%. The exact target value is determined individually for each patient.
HbA1c for follow-up
False all-clear possible
Unfortunately, if the HbA1c is normal, this does not automatically mean that the blood glucose situation is good. A brief elevation in blood glucose (less than four hours) does not affect the HbA1c. It is therefore quite possible that nerves and blood vessels have already been damaged by the high sugar, without it being noticeable in the laboratory findings.