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October 13, 2003

A1c (Glycohemoglobin, HgbA1c)

Question from Pennsylvania, USA:

My 13 year old son, diagnosed about five months ago, had an A1c of 10% at diagnosis; six weeks later, it was 8.6%, and last week it was 8.3%. I was disappointed, surprised, and confused that his A1c dropped 2% only six weeks after diagnosis with high blood sugar numbers, but only 0.3% after three months of excellent blood sugar readings (with the exception of two weeks of intermittent highs). How can this be? Can you provide an explanation?Could eating immediately before an A1c test or have wet alcohol from swabs on fingers alter an A1c test? I am assuming the answer is no, but I had to ask.


Interesting question, but I’m not sure I know the answer. Of course, the most common explanation is that your son’s control was not as good as you thought it was after the six-week check up. Remember that home glucose monitoring, even done four to six times daily, is only checking the glucose for that moment in time. What is the glucose doing the other 1436 minutes of the day? That is one of the purposes of the A1c. Could the A1c be wrong? Sure. No blood test is infallible.

Since the A1c reflects the average blood glucose over the previous three-month period, if the home glucose readings are not in sync with the HbA1c, one should question the results of the meter or consider a lab error for the HbA1c. Other (rather uncommon) factors can disrupt the HbA1c result (e.g., certain types of anemia can do so).