Background and ObjectivesThe aim of the 18th Platelet Immunology Workshop was to characterize platelet‐reactive alloantibodies by the use of in‐house MAIPA protocol and/or commercial platelet antibody testing kits, to identify whether anti‐HPA‐1a quantification could be compared between laboratories, to evaluate whether a protease inhibitor could preserve CD109 and the expression of the HPA‐15b antigen and to prove HPA genotyping methods.Materials and MethodsWorkshop materials (plasma samples, DNA and additional reagents) were shipped by the Organizing Laboratory in Stockholm, Sweden. Thirty‐two laboratories from 19 countries participated in the 18th International Platelet Workshop.ResultsA majority of the laboratories agreed on the serological identification of anti‐HPA‐1a and anti‐HPA‐5b antibodies. For the quantification of anti‐HPA‐1a, however, the result differed greatly between the laboratories with high coefficient of variation and the lowest concentration 0·5 IU/ml not detectable. Furthermore, false‐positive reactions due to cross‐reactivity with other glycoproteins did often interfere with the serological evaluation of anti‐HPA antibodies. Detection of anti‐HPA‐15 antibodies remains challenging; the addition of a protease inhibitor did not seem to preserve HPA‐15 expression on platelets. For genotyping, correct results were achieved in four of five samples. A mutation near HPA‐3 in one sample caused false interpretation of the typing results from five laboratories.ConclusionsThis workshop has identified three specific areas in platelet serology with need for improvement: methodology amendment to reduce non‐specific binding and cross‐reactivity; standardization of antibody quantification (such as anti‐HPA‐1a); and detection of anti‐HPA‐15 antibodies. The use of universal monoclonal antibodies for antigen capture assays as well exactly defined references of well‐defined specificity and concentration should be envisioned.