Collaborative studies to establish the first World Health Organization International Standard for detection of human antibody against human platelet antigen‐3a

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Abstract
Background and Objectives  The platelet‐specific antibody anti‐human platelet antigen‐3a (anti‐HPA‐3a) is involved in neonatal alloimmune thrombocytopenia, post‐transfusion purpura, and platelet refractoriness. However, HPA‐3a antibodies are often difficult to detect, probably because the antigen is labile. This report describes the production of a freeze‐dried preparation of pooled human plasma, coded 03/190, containing IgG antibodies against the HPA‐3a. The material is intended for use as a minimum sensitivity reagent in glycoprotein‐specific assays currently used for anti‐HPA‐3a detection. Laboratories can use it to assess the sensitivity of their ‘in‐house’ assays for anti‐HPA‐3a and to calibrate local controls for routine use in each batch of tests.Materials and Methods  Plasma containing anti‐HPA‐3a was obtained from a mother of two babies both born with severe thrombocytopenia, and following dilution it was freeze dried in glass ampoules.Results  Two collaborative studies demonstrated that the candidate material contained anti‐HPA‐3a and human leucocyte antigen (HLA) class I antibodies, but no other HPA antibodies that might confuse the detection of the anti‐HPA‐3a. The minimum dilution that should give a positive result was determined to be 1 : 8 by two further international collaborative studies involving a total of 49 laboratories in 23 countries.Conclusion  The material also contains HLA antibodies and is suitable for use only in techniques that are glycoprotein specific (i.e. monoclonal antibody immobilization of platelet antigens and enzyme‐linked immunosorbent assay) where only HPA antibodies will be detected. This standard will allow laboratories to measure their sensitivity of detection of anti‐HPA‐3a and will also allow those laboratories with relatively insensitive techniques to monitor their performance as they improve their methodology.