Vitamin B12 quality control trials.

The results of regional quality control trials of vitamin B12 assays are reported. Consideration is given to the materials suitable for such trials. The technical and clinical performance of the participants are assessed together with the methods used. The introduction of a target coefficient of variation has produced better identification of good and bad performance and the use of a reference serum has permitted comparison of assays of different methods. The linearity of most methods is suspect and indicates the need for reference sera of varying concentration. Introduction of kits has not generally improved precision and variation between laboratories shows the use of kits can be improved.