Evaluation of an enzyme-linked immunosorbent assay kit (GTI PakPlus (R)) for the detection of antibodies against human platelet antigens

Twenty-six serum samples from 24 patients were investigated for the presenc e of platelet-specific antibodies in a partly retrospective (n = 15) and pa rtly prospective (n = 9) study. The sera contained either alloantibodies to human platelet antigens (HPA) (n = 23) or were from clinically suspected c ases of fetomaternal alloimmune thrombocytopenia (FMAITP) in which platelet -specific antibodies had not been detected (n = 3). Three techniques were u sed to detect platelet antibodies: the platelet immunofluorescence test, th e monoclonal antibody immobilization of platelet antigens (MAIPA) assay and a commercially available enzyme-linked immunosorbent assay - GTI PakPlus(R ) (GTI kit). Two alkaline phosphatase-conjugated antiglobulin reagents prov ided by the manufacturer were used in the GTI kit: an antihuman IgG/IgA/IgM (IgGAM) conjugate and an antihuman IgG conjugate. The GTI kit with the ant i-IgGAM conjugate failed to detect eight antibody specificities in seven se ra (anti-HPA-la [n = 3], anti-HPA-3a [n = 1], anti-HPA-3b [n = 1] and anti- HPA-Sb [n = 3]). Greater signal-to-background ratios were achieved in the G TI kit with the anti-IgG conjugate but five antibody specificities (anti-HP A-la [n = 1], anti-HPA-3a [n = 1]. anti-HPA-3b [n = 1], anti-HPA-Sb [n = 2] ) remained undetectable. All the sera were detected by MAIPA assay and, fur thermore, the MAIPA assay achieved the greatest signal-to-background ratio in the majority of sera tested. These findings re-emphasize the value of th e MAIPA assay in reference laboratories and illustrate that the GTI kit may either fail to detect or incorrectly identify clinically significant HPA a ntibodies.