An international proficiency study with the tumor marker CA 125.

A strict and adequate quality assurance program is the only real guarantee of the reliability of laboratory test results. Such proficiency testing was carried out for the CA 125 test system in five university laboratories over a period of three years (1984-1987) using five different reference materials (BIOREF, FRG). A concentration-dependent performance profile could thus be established evaluating a total of 301 assays. Intra-assay precision of the test ranged between 4.8 and 11.5%, and interassay precision between 13.6 and 19.1%. Laboratory specific average values of the individual reference materials ranged between 26 and 32 U/ml for reference 1, 51 and 59 U/ml for reference 2, 109 and 121 U/ml and 193 to 240 U/ml for references 3 and 4, respectively. Mean values for reference 5 ranged between 401 and 458 U/ml. There was no significant difference between mean values for the laboratories. Considerable batch-dependent variations of values became evident during the study but these were not indicated by the kit control supplied by the manufacturer. During the whole investigation period no systematic drift in values could be observed using trend analysis, indicating excellent stability of the reference material if stored frozen (-20 degrees C).