Serum platelet antibody testing: evaluation of solid-phase enzyme immunoassay and comparison with indirect...

We compared the ability of solid-phase enzyme immunoassay (SPEIA) with that of indirect immunofluorescence to detect serum platelet antibodies by parallel testing five sets of serum specimens: (1) 12 monospecific HLA class I specimens with defined specificities, (2) 4 HPA-1a specimens, (3) 164 sequential unselected specimens sent to our laboratory for serum platelet antibody testing, (4) specimens from 15 consecutive patients sent for indirect immunofluorescence testing alone, and (5) specimens from 19 consecutive patients sent for both indirect and direct immunofluorescence testing. In addition, specimens of HLA sera were tested by standard complement-dependent lymphocytotoxicity. Solid-phase enzyme immunoassay was consistently more sensitive than indirect immunofluorescence for all 12 HLA specimens and more sensitive than complement-dependent lymphocytotoxicity for 11 of 12 specimens. Similarly, SPEIA was more sensitive than indirect immunofluorescence for all four HPA-1a serum specimens by one to three dilutions. In the nine presumed autoimmune cases (group 5), results were positive with SPEIA in one case; no positive results were noted with indirect immunofluorescence. The solid-phase enzyme immunoassay test permits ready differentiation between alloantibodies directed to HLA and those directed to platelet-specific glycoproteins.