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

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.