Partial C antigen in sickle cell disease patients: clinical relevance and prevention of alloimmunization.

BACKGROUND: Partial Rh antigens have been widely described in black individuals. Carriers are prone to immunization when exposed to the normal antigens. In sickle cell disease (SCD), patient alloimmunization is a major cause of transfusion failure. The potential of individuals with partial C antigen to make anti-C has not been investigated. We sought partial C status and anti-C production in a cohort of SCD patients with the C+ phenotype, to determine whether exposure to normal C antigen should be avoided. STUDY DESIGN AND METHODS: We constituted a cohort of 177 randomly selected SCD patients expressing C antigen. We screened for (C)ce(s) and R(N) haplotypes, presumably associated with partial C antigen in Afro-Caribbeans, and we recorded the number of transfused C+ red blood cell (RBC) units, immunization status, and extended phenotype.
RESULTS: Forty-nine patients carried abnormal C antigen, deduced from the presence of (C)ce(s) and/or R(N), not compensated by a normal RHC allele in trans. Among patients with partial C phenotype exposed repeatedly to C+ RBCs, 30% produced anti-C. Two patients experienced hemolysis. In our hospital, with 22% of SCD patients expressing C, prevention of anti-C immunization for all individuals with partial C antigen would require a 7% increase in the use of C- RBC units. These RBCs are already in short supply for SCD patients who are C-.
CONCLUSION: This study demonstrates the need to detect partial C within C+ SCD patients and to prevent immunization. A larger number of Afro-Caribbeans donors is needed to provide these patients with C- RBCs.