I recently moved and changed endo’s. My previous doc used a device in the office to get an “instant” (about 10 minutes) A1C reading from a fingerstick. He also has A1C tests done by a lab as part of other bloodwork (from the vein). My new endo only has me go to a lab to have A1C tests done. When I was in pediatrics (1981-1990) my doctor not only had me go to a lab, which was the only option at the time, but said to always go to the SAME lab because of fluctuations between the two.
My perception is that the A1C done by a lab from the vein can be higher, by about 0.3 to 0.5. Since my new doc has always given me results over 7.0, while the previous one always gave me results under 7.0, it’s a bit disconcerting. (Fortunately, I got my life insurance based on the fingerstick, sub-7 numbers!)
Is there a noted, documented variation between the two? Does one test have more of a tolerance than another (meaning: if two tests were done within 5 minutes of each other, how difference would they be?)
Not all A1cs are equal. There has been increasing efforts to make A1cs standardized and control the variation and error in the tests. It is only recently that the tests have reached the point of being accurate enough for real usefulness. The goal is in 2011-2012, to have certified A1c testing methods be accurate within 7%, which means that a true reading of 7% could be acceptably tested and provide the result of either 6.5% of 7.5%. As far as I am concerned, that still s*cks big time and can be the difference between an “atta boy” and being berated by your doctor.
That being said, some of the instant tests are “ok” others don’t even meet the basic criteria above. A summary of recent results can be found at the ngsp.org site. It should be noted that the Bayer A1cNow showed some real problems for patients using EDTA as an anticoagulant. If you look at the results, you will see that many labs showed a significant and consistent bias (always testing high or low).
I do not know the answer but want to give some input- I keep detailed reports and logs and before the CGM tested 6-8times a day wrote down when and what I ate how much insulin how far and long I ran and the Doc said I was doing great but then blood from the vein shows me with a high A1C and the Doc said the two did not match up at all? so now with the CGM we are hoping to find the issue - but if the A1C from the vein is high that might answer it too
Finger sticks versus HPLC measurement can vary widely. Like he said the labs make a huge difference. The best you can do is be consistent with what lab everything is going to and keep good control. A1C is just a number, but decreased variability in in the daily measurements is more important than having a slightly higher BG. Having a BG ranging from 50-200 in the same day will give you an average of 125, the same as if you are 100-150. However, long term complications are more apparent with the 50-200 group even though they will have the save overall A1C.
