[Basic and clinical evaluation of an immunoradiometric competitive inhibition assay for sialyl Tn antigen: (1). Evaluation of assay conditions and normal values. STN Study Group].

An immunoradiometric competitive inhibition assay of the serum levels of the sialyl Tn antigen using "STN Otsuka" kits is described. The assay required only duplicate 50-microliters samples, and the concentration of sialyl Tn antigen in serum was determined by reference to a standard curve ranging from 0 to 400 arbitrary units/ml. The intra-and inter-assay reproducibilities were largely satisfactory. The serum levels of the antigen in normal individuals were not affected by ABO and Lewis blood type status of the tested individuals. Normal values were 25.5 +/- 9.8 in male, and 21.3 +/- 8.0 in female, and the difference was statistically significant at p less than 0.001. The serum level of the antigen was not affected by menstrual cycle or pregnancy in female, whereas the level of other tumor markers such as CA 125 was highly variable depending upon these conditions.