Collaborative studies to establish the first WHO Reference Reagent for detection of human antibody against human platelet antigen‐5b

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Abstract
Background and Objectives This report describes the production of a freeze‐dried preparation of pooled human plasma, coded 99/666, containing immunoglobulin G (IgG) antibodies against human platelet antigen 5b (HPA‐5b). Materials and Methods The material is intended for use as a minimum sensitivity reagent in the assays currently used for detection of antibodies to HPA‐5b. Laboratories can use it to assess the sensitivity of their ‘in‐house’ assays for antibodies to HPA‐5b and to calibrate local controls for routine use in each batch of tests. Results Two collaborative studies demonstrated that the two candidate materials contained antibodies to HPA‐5b and that there were no other HPA or human leucocyte antigen (HLA) antibodies which might confuse the detection of antibodies to HPA‐5b. The two samples were pooled and freeze‐dried in 1‐ml ampoules. Conclusions The minimum dilution of the antibody against 5b required to yield a positive result was determined, by two international collaborative studies involving a total of 49 laboratories in 26 countries, to be 1 in 2.