Platelet Antibody Specificity Analyzed by Different Tests

The serum samples were tested for Human Leukocyte Antigen (HLA) or platelet-specific antibodies. The scientists routinely use two commercially available test methods, an antigen capture ELISA and a solid-phase assay. For the confirmation and specification of anti-HLA class I antibodies, a complement-dependent lymphocytotoxicity test is additionally performed.

All serum samples were analyzed by enzyme-linked immunosorbent assays (ELISA), either Lifecodes PAKPLUS or PAK12 (Gen-Probe; Waukesha, WI, USA), and by a solid-phase assay (Capture-P Ready Screen, Immucor Inc.; Norcross, GA, USA), and in specified cases by a specific lymphocytotoxicity test (LCT, Bio-Rad Medical Diagnostics GmbH; Dreieich, Germany). The LCT was performed in cases of clinically suspected or, by the described assays detected, HLA class I antibodies.

Platelet antibodies were detected in 366 of 1,234 samples (29.7%). In 70.3% concordant negative, but only in 8.4% concordant positive results were obtained with both the methods; 185 of 1,053 in the solid-phase assay negative samples were positive in the ELISA (15.0%). In samples positive in both methods, most antibodies reacted against HLA class I antigens. Glycoprotein (GP) specific platelet antibodies were more frequently detectable in the ELISA than in the solid-phase assay, whereas weakly positive results have to be interpreted cautiously.

The authors concluded that because ELISA, solid-phase assay, and LCT showed highly divergent results and only for detecting soluble platelet antibodies, and due to several limitations. The additional analysis by the “monoclonal antibody-specific immobilization of platelet antigen” (MAIPA) assay is highly recommended. The study was published on May 5, 2015, in the Journal of Clinical Laboratory Analysis.

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