Background and objectives: The aim of the 13th International Society of Blood Transfusion Platelet Immunology Workshop was to compare the sensitivity and specificity of the in-house method for the detection of human platelet antigen (HPA) antibodies currently used in participating laboratories with a modified rapid protocol for the monoclonal antibody (mAb) immobilization of platelet antigen (MR-MAIPA) assay.
Materials and methods: Twenty-eight laboratories from 15 countries participated. A set of four freeze-dried minimum potency reference reagents with known single-specificity HPA antibodies were supplied for testing by titration with both assays and two coded freeze-dried plasma samples were provided for antibody specificity testing. Critical reagents and materials for the MR-MAIPA were provided including lyophilized panel platelets and five capture mAbs.
Results: Titration of the reference standards showed that the sensitivity of the MR-MAIPA was the same as the in-house methods. The proposed replacement anti-HPA-1a reference reagent 05/106 gave results that did not differ significantly from the current reference reagent 93/710. The results with the two blinded samples showed that in the first sample, 27 out of the 28 laboratories were able to correctly identify the anti-HPA-1a present when using their respective in-house methods, but only 23 correctly identified the antibody when using the rapid MAIPA method. The results from the second sample, which contained multispecificities, showed that only 50% of the participants correctly identified all five antibodies present using their in-house method. The results for the rapid MAIPA were lower, with only 32% identifying all specificities. The variability in the reconstitution of the freeze-dried platelets may have been one of the contributing factors to the poorer results.
Conclusions: The sensitivity of the MR-MAIPA compared favourably with that of the in-house methods. Most laboratories were able to identify anti-HPA-1a alone in Sample 1 but more than half of the participants were not able to correctly assign the specificity of all HPA antibodies present in the second sample. The usefulness of the panel of freeze-dried platelets varied considerably between laboratories.