February 6, 2004
A1c (Glycohemoglobin, HgbA1c)
Question from Pennsylvania:
The A1C test result at our most recent quarterly endo visit for my 14 year old was 8.7. However only two weeks ago, we completed an at home A1C from Metrika (A1cNow) with a result of 7. Can you explain the diverse test results only 2 weeks apart? My endo offered no explanation when we shared we got a 7 only two weeks before.
When you compare the two A1c results, you have to understand that this assay is not nearly as precise a one, as say a blood urea, and also that the two separate methodologies may have very different fundamentals and degrees of variance. These figures are in fact published regularly for a variety of A1c procedures as part of the CLIA (Clinical Laboratory Improvement Act) proficiency testing program. In a doctor’s office or a clinical laboratory where routine this testing is obligatory and where one person does all the testing, the DCA 2000 device, which is one of the most used, will show 95% confidence limits of about 8%. This figure increases if more people perform the test. I don’t know what the figures are for ‘A1cNow’; but I suspect that they are greater. What this means is that to interpret A1c results you need to stay, as far as possible, with one laboratory and to look at each result in comparison with an imagined regression line through a number of previous points. To put all this more simply, I believe that the different test results are technical and do not reflect any real difference in the degree of control.