Is poor glycemic control associated with reduced red blood cell lifespan?

A major assumption in the interpretation of HbA1c as a measure of glycemic control is that the duration of Hb exposure to glucose does not vary among patients who are hematologically normal. In this issue of Diabetes Care, Virtue et al. (1) use an appealingly simple method to quantitate erythrocyte lifespan (2,3) and report an inverse correlation with glycohemoglobin concentration in patients with diabetes. They interpret this as a reduced erythrocyte lifespan at higher blood glucose concentrations. The calculation of erythrocyte lifespan depends on Hb concentration and the amount of carbon monoxide (CO) in exhaled air and in atmospheric air collected at the subject’s home just after awakening. The principles behind the method are that heme catabolism is the only endogenous source of CO and that erythrocytes removed from the circulation are the major source of heme. However, there are multiple assumptions behind the methodology, which may not be met, in the complicated scenario of diabetes. These all come together in Eq. 1 of Virtue et al. (see [1] for the definition of terms)