What is HbA1c?
HbA1c is a glycated hemoglobin, that is a form of hemoglobin (hemoglobin) bound to the glucose (glycation). The coupling of glucose to hemoglobin A takes place without enzymes (Amadori rearrangement), therefore it is not a glycosylation.
The percentage of HbA1c in the total hemoglobin (Hb) can be detected in blood tests. It provides information about the blood glucose levels over the past four to twelve weeks (an average of eight weeks, which is about the average age of erythrocytes) and is therefore commonly referred to as long-term blood sugar or blood sugar memory.
Units
The HbA1c level in the blood is expressed as a proportion of total hemoglobin in percent or parts per thousand (mmol / mol). However, there are various Glykierungsprodukte, since it is a non-specific reaction. To standardize the measurement world, a working group of the IFCC (International Federation of Clinical Chemistry and Laboratory Medicine), the HbA1c defined as the product of a stable coupling of glucose to the N-terminal valine of the beta chain of hemoglobin A1.
Commonly used is still an indication in percent (%). Introduced by recommendation of IFCC international unit is mmol / mol hemoglobin, so a blood alcohol value. After a guideline of the German Medical Association April 1, 2008, the HbA1c value should now also be specified in this unit. For better distinction of the% specification, this value can also be referred to as HbA1cM. The conversion formula is:
HbA1c [mmol / mol Hb] = (HbA1c [%] - 2.15) x 10.929
Sample collection (pre-analysis)
The HbA1c is determined from whole blood, which usually contains EDTA as an anticoagulant. Requirements for storage and treatment of the sample material depend on the analysis system used. Usually, the sample is one to two weeks stored at 4 ° C or can be stored for several months at -20 ° C.
Laboratory diagnostics
To measure the value today predominantly laboratory automation be used to process the photometric measurement process fully automatically in microtiter plates. The modern instruments are now using monochromatic light-emitting diodes instead of (broadband) halogen lamps. LEDs have the advantage that hardly any heat in the device and thus no cooling of the machine is necessary. Thus, you can work with less reagent and sample volume - which represents a significant cost advantage for the user.
When measuring an enzyme immunoassay principle is used. This method of measurement results for single measurements make significant difference, by measuring a plurality of identical samples in microtiter plates can be personalized with computational methods, however, identify sufficiently reliable averages.
Normal range and interpretation
The normal range is 29 to 42 mmol / mol Hb and 4-6 percent.
False high HbA1c is measured in iron deficiency anemia, as in this case, the degradation of erythrocytes is slow.
Falsely low values may occur in hemolytic anemia, liver cirrhosis, thalassemia, chronic renal failure and increased de novo synthesis of erythrocytes. The values can also be distorted by a greater loss of blood or a blood transfusion.
Diabetes mellitus
A lying within the normal range HbA1c includes diabetes mellitus not. However, values over 6% support a suspected diagnosis.
The HbA1c is measured in patients with diabetes mellitus every three months. The goal of therapy is that the HbA1c remains below 7-8% in order to delay the possible long-term consequences of this condition as long as possible or avoid.
In individual cases, the determination despite NGSP standardization still show strong method-dependent differences. It is therefore recommended to monitor a patient always with the same method.