Non-D Rh antibodies appearing after apheresis platelet transfusion: stimulation by red cells or microparticles?

Background Apheresis platelets (APs) have gained favour over whole blood-derived platelets on the presumption that they are less likely to provoke alloimmunization to red-blood-cell antigens. Case Reports Non-D Rh antibodies appeared in three patients after apheresis platelet transfusion. Anti-C and anti-E arose in two female patients with previous antigen exposure. Both anti-c and anti-E arose in a male recipient with no prior transfusion history. Materials and Methods Fifty APs were analysed for residual RBCs and RBC-derived microparticles, using samples obtained from a local blood centre. Cells and microparticles were quantified with a flow cytometry gating scheme, using PE-labelled anti-CD235a (glycophorin A) and FITC-labelled anti-CD41a (platelet gp IIb/IIIa) to distinguish lineage. Results Apheresis platelets were found to contain a mean of 7 center dot 5 x 106 (95% C.I. [6 center dot 3-8 center dot 5 x 106]) RBCs on one manufacturer's device and 5 center dot 2 x 106 (95% C.I. [4 center dot 0-6 center dot 3 x 106]) RBCs on another's. RBC-derived microparticles averaged 210 center dot 7 x 106 (95% C.I. [166 center dot 2-254 center dot 2 x 106]) on one manufacturer's device and 232 center dot 3 x 106 (95% C.I. [194 center dot 3-272 center dot 9 x 106]) on another's. These counts all correspond to volumes of < 1 mu l. Conclusion Despite RBC contamination of APs below commonly accepted thresholds for Rh immunogenicity, AP transfusion can provoke non-D Rh antibody formation. RBC-derived microparticles, smaller but more numerous than RBCs, are volumetrically comparable and may be a hitherto underappreciated antibody stimulus. Further microparticle research will guide considerations of extended phenotypic matching of platelet components.