A simple and rapid competitive enzyme-linked immunosorbent assay to identify HPA-1a (P1(A1))-negative donor platelet units

Background: Alloantibodies to HPA-1a (Pl(A1)) are the major cause of neonatal alloimmune thrombocytopenia and posttransfusion purpura and have been implicated in refractoriness to random-donor platelet transfusions. However, most assays used to phenotype platelets are cumbersome or time-consuming for large numbers of samples. Study Design and Methods: A simple, competitive (inhibition) enzyme-linked immunosorbent assay for HPA-1a phenotyping of donor platelets was developed. A segment from the donor platelet unit transfer line was sealed to obtain a small aliquot of platelets, These platelets were washed once and added to a predetermined dilution;of serum containing alloantibodies to HPA-1a. Residual anti-HPA-1a binding to the glycoprotein IIb/IIIa purified by lectin and high-performance liquid chromatography and coated on microtiter wells was detected with a conjugated anti-human IgG. A lack of inhibition equivalent to control (no platelets) was used to determine that the platelets were HPA-1b/b. Results: Of the 557 platelet units tested, 14 (2.5%) were found to be HPA-1a negative, and they were confirmed to be HPA-1b/b by DNA genotyping. Two of the 14 HPA-1b/b units were also HPA-3b/b (approx, 0.35% of the random population), Use of the microtiter format allows 100 to 200 samples to be processed per day. Conclusion: This simple and inexpensive assay is useful for identifying HPA-1b/b units for platelet-compatible transfusions or for platelet antibody investigations.