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June 26, 2000

A1c (Glycohemoglobin, HgbA1c)

Question from Neuchatel, Switzerland:

I have a friend who has diabetes. I'm interesting in the monitoring of glycosylated hemoglobin and I'm wondering how it is possible to separate the glycated hemoglobin from the native one. I think that in the main part of the tests HPLC is used for this purpose but it will be great if I can see a chromatogram of the two separated peaks (if this is the case). Where I can find this chromatogram? Can you help me?

Answer:

The first point I would like to make is there are a variety of assays for A1c each one of which has its own normal range and coefficient of variation. The College of American Pathologists in its last proficiency testing report listed eight of which the Bayer DCA 2000 monoclonal antibody assay was the most accurate giving 95% confidence limits of +/- 7%, a figure which is almost certainly higher in routine work. The most popular unit was the Abbott IMX (HbA1c) which had a 95% confidence limit of +/- 32%. So your friend needs to find out which method her doctor is relying on and then to look at serial levels rather that the immediately recent one.

If you are near to a medical library you might like to look at a paper which summarises this by Hosseini, HH. et al in Metabolism 48:1498 (1999). HPLC is still used in some very high volume laboratories and depending on the gel used can measure many other hemoglobins especially fetal hemoglobin which used to be a common source of misinterpretation (see Ou, CN. in Clin.Chem. 39:820 (1993), Nowadays in the US instruments like the Bayer 2000 have taken priority over HPLC primarily because of the fact that a result becomes available in a few minutes at the time of the clinic visit.

In brief, A1c levels are no longer reported as chromatogram peak areas or heights though I am sure you could get the information from the supplier of whatever method is used for your friend.

DOB