I once dated a girl who was a lab tech at a hospital. She had very strict guidelines about calibrating the equipment for running blood tests (like an HbA1c, among others). My first though when I read about the major difference between the two sets was perhaps a calibration issue?
In any case, it is definitely unfortunate that we (as people living with this disease, as well as our physicians and other healthcare team members) put so much clout in a number that appears to be a moving target w/ regard to reproducibility. Much like making corrections or bolus calculations using the BG numbers on our glucometers at any given moment (that by regulation standards only have to be within +/- 20% accuracy)...
Outside of the calibration issue, I don't really have any good suggestions for valid reasons. I'm definitely interested in hearing what others might have to say though, because like you, I thought that a1c had a bit more accuracy than that.
One thing we all seem to forget about is that machines operate to only a certain degree of accuracy, and there is always a margin of error. I don't know how much is allowed by the FDA on the A1c machines, but NO machine is absolutely precise. Also, I don't trust the in-house machines at all, because although they are reasonably accurate much of the time, there ARE inaccurate results, and I don't know how often they occur, but I know they do.
None of those results would be any cause for worry, though, because they AREN'T high numbers, and the only real assessment of your control is frequent testing at appropriate times -- before meals and 2 hours after meals (to find the peak), and before and after exercise, during illness and stress and before bed, and sometimes in the middle of the night. That's a lot of testing, but it will tell you what you need to know and can control.
And just for perspective, my A1c is ALWAYS lower than what I would expect, so I just use it as a comparison with myself, and know that my goal needs to be lower than most people. Don't always achieve it, but all these numbers do is tell you if you need to tweak treatment (and at your numbers, I doubt your doc would want you to). Otherwise, they're just numbers, and there is a whole lot more to consider than just numbers!
Just for the record:
Both the 6.0 and 6.3 was analyzed at a lab and not done with those in-house machines. The 5.7 was from an in-house machine, the same blood sent to a lab came back with a 5.5-result.
My hospital tells me that the test results are not at all precise, and my diabetes nurse would have me believe the results could vary just as much as glucometer and CGM results vari\y, namely plus/minus 20 percent which your test results show.
I have now talked to a friend of mine. Her profession actually include development of the in-house-machines. She told me that hba1c-results no matter what kind of equipment you use are not allowed to differ more than +/- 0,1. This goes for Norway, don´t know what the FDA guidelines are, but usually your guidlines are more strict than ours.
Sadly, the A1c is not particularly accurate. Things are improving, and I give a lot of credit to a CDC program called the National Glycohemoglobin Standardization Program (NGSP). In 2011-2012, the NGSP sought to bring laboratory A1c tests within +/- 7% (in 2007, it was a horrible +/- 15%). By the end of 2013, they hope for +/-6 %.
You can look at the latest calibration results, and while most lab testing equipment meets the standards, the Bayer A1cNow is not particularly accurate.
ps. A +/- 7% variation on an A1c of 7% means that your result could be anywhere in the range 6.5 - 7.5%.
Yes, you´re right. Found the same:
"According to the National Diabetes Information Clearinghouse (NDIC), the “official” accuracy of the A1C test result is 0.5 on either side of the “true” number. So if your honest-to-God A1C was 7%, then you could expect your lab test to read anywhere between 6.5% and 7.5%."
More on hba1c "here:http://www.diabetesmine.com/2013/01/ask-dmine-follies-of-the-a1c-te...