The World Health Organization International Collaborative Study for Islet Cell Antibodies

Aims/hypothesis. Islet cell autoantibodies are a specific marker for Type 1 (insulin-dependent) diabetes mellitus. Standardisation of islet cell antib odies and the uniform reporting in International units is critical to resea rch and the development of assays for islet cell autoantibodies as diagnost ics. Methods. The suitability of a candidate serum to serve as the international standard for islet cell antibodies was studied by 19 participants in 8 cou ntries. In addition, the purpose was to investigate whether the serum could also serve as a standard for antibodies to the 65 000 M-r isoform of gluta mic acid decarboxylase (GAD65) and islet antigen-2 (IA-2). Control sera wer e included in the study to assess the validity of the various assay systems . The sera were lyophilized to World Health Organization criteria and the c andidate serum assigned the ampoule code number 97/550. Results. The use of 97/550 was shown to notably reduce inter laboratory var iability in the measurement of islet cell antibodies. In addition, there wa s a pronounced reduction in inter laboratory variability in the measurement of GAD65 and IA-2 antibodies. Conclusions/interpretation. On the basis of the results reported here and w ith agreement of the participants, the preparation 97/550 has been establis hed by the World Health Organization Expert Committee on Biological Standar ds for establishment as the first international standard for islet cell ant ibodies, with an assigned potency of 20 international units. In addition, 9 7/550 can serve as an international reference reagent for specific GAD65 an tibodies, with an assigned potency of 100 units. It can also serve as a Nat ional Institute of Biological Standards and Control (NIBSC) reference reage nt for IA-2 antibodies for evaluation of assays for this material.