Response: Other factors may contribute to differences between sickle cell and non–sickle cell patients

We appreciate the comments by Dr Mintz concerning the differences in alloimmunization rates reported for sickle cell patients and our findings based on data that excluded sickle cell patients.¹  In planning our analysis, we did not expect sickle cell patients to differ from the general population. However, we excluded sickle cell patients because our study hospitals prospectively matched for the C, E, and K antigens for sickle cell patients and no other patients. Because we did not analyze sickle cell patients, we do not have direct evidence to explain the apparent differences we saw in the non-sickle cell patient population and those reported by others in sickle cell patients.

While differences in antigen frequencies between racial groups might explain such a difference, our preliminary analysis does not find a significant difference in the alloimmunization rates of African-American patients who do not have sickle cell disease and that of the general patient population at our adult study hospital. Hence, we suspect other factors contribute to apparent differences between sickle cell disease patients and other patients but we have no evidence to support or refute any such factor.