Collaborative study to establish the first international standard for quantitation of anti‐HPA‐1a

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Abstract
Background and Objectives This report describes the production of a freeze‐dried preparation of pooled human plasma, containing immunoglobulin G (IgG) antibodies against the human platelet antigen 1a (HPA‐1a). The material, coded 03/152, is proposed as an International Standard containing 100 arbitrary units of anti‐HPA‐1a for use in quantitative assays to determine the anti‐HPA‐1a activity in clinical samples. Materials and Methods Plasma samples containing potent anti‐HPA‐1a were pooled and freeze dried in 1‐ml ampoules. In addition, three individual plasma samples were selected which had varying levels of anti‐HPA‐1a activity. The anti‐HPA‐1a activity of these three samples was determined by using a variety of quantitative assays with the proposed standard as a reference. Results An international collaborative study, which was part of the 2004 ISBT Platelet Immunology Workshop, involved 39 laboratories in 24 countries and showed that the anti‐HPA‐1a activity in three test samples could be reliably determined by using the proposed standard. Conclusions Laboratories can use this standard to measure the anti‐HPA‐1a activity in patient's samples. Further studies are required to determine the relationship between anti‐HPA‐1a activity and clinical outcome in patients with neonatal alloimmune thrombocytopenia (NAIT).