Does Variation in Mean Red Cell Age Impact HbA1C Interpretation?

Prevention of complications in veterans with diabetes depends heavily on assessment of blood glucose and HbA1c. The HbA1c is a blood test that measures the exposure of hemoglobin (Hb) to a person's average blood glucose over the lifespan of a red blood cell (RBC). The test is heavily relied upon as a measure of blood glucose control. It is normally assumed that all people (those with and without diabetes) have a narrow range of red blood cell survival. It has been recently shown that this is not a valid assumption. A more precise test of red blood cell survival, using a biotin label method, demonstrated a substantial difference of red blood cell survival among otherwise normal people. There is sufficient difference in red blood cell survival to alter the estimate of glycemic control from the HbA1c test by as much as 30 per cent. This introduces concern that HbA1c values do not mean the same thing in a significant number of people. Although the evidence is clear that there is variation in RBC survival among people, attributing this variation to differences between individuals depends on answering several simple questions which surprisingly remain unanswered: whether RBC survival is stable over time within an individual and whether blood glucose control affects its stability. Therefore, the goal of the proposed studies is to define these characteristics.