Limits of the MAIPA assay when differentiating high-titered platelet-reactive antibodies.

Experience with the MAIPA assay for the diagnosis of platelet-reactive antibodies has shown that high-titered antibodies falsify the test results. We here demonstrate 2 cases: i) A serum with high-titered HLA antibodies (100% panel reactivity in the LCT, titer between 4,000 and 12,000), and ii) Serum with a high-titered anti-HPA-1a (titer in the MAIPA assay 1,000). In both cases, it can be demonstrated that these antibodies led to unspecific reactions. In the 1st case, they interfered with the diagnosis of additional platelet-specific antibodies. Only the use of HLA-compatible platelets allowed a correct identification. On the other hand, in the high-titered anti-HPA-1a unspecific reactions were seen with the glycoproteins Ib/IX, Ia/IIa, and beta 2-microglobulin, leading to misinterpretations. These examples demonstrate that, in the test conditions as described, a correct diagnosis of high-titered sera might only be achieved by using compatible HLA or HPA cells.