Platelet Antibody Specificity Analyzed by Different Tests

The detection of platelet antibodies plays a crucial role in the diagnosis of immunologic platelet disorders such as fetal/neonatal alloimmune thrombocytopenia (FNAIT) or refractoriness to platelet transfusions, influencing further therapeutic management.

The gold standard analysis for the determination of platelet antibodies, the “monoclonal antibody immobilization of platelet antigens” assay is restricted to specialized reference laboratories due to the laborious efforts involved and the consequent need for freshly prepared test platelet.

Hematologists at the Medical University of Graz (Austria) analyzed serum samples from 1,234 patients with a median age of 58.2 years and 573 were female and 661 male. 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.

Related Links:
Medical University of Graz 
Gen-Probe 
Immucor Inc.