Basic evaluation of an immunoradiometric competitive inhibition assay for sialosyl‐Tn antigen in sera in women assay conditions and normal values

The assay conditions needed for an immunoradiometric competitive inhibition assay of sera in healthy women were studied using the monoclonal antibody TKH2, which is known to recognize specifically sialosyl‐α2,6‐GalNAcα1‐0‐serine/threonine (S‐Tn) antigen, a mucinous cancer‐related antigen. Stable results were obtained with an incubation time of 1.5 hours at room temperature. The intra‐assay and inter‐assay coefficients of variation were 3.27% and 3.07%, respectively. The mean (± standard deviation [SD]) levels of serum S‐Tn in 602 healthy women was 21.2 U/ml (±8.4 U/ml). Values showed a normal logarithmic distribution. Although slightly higher levels were seen in postmenopausal compared with premenopausal women, the differences were not significant. The cutoff value of 41 U/ml was determined from data obtained in 602 healthy women; higher levels were observed in only 2%. Serum S‐Tn levels were not strongly influenced by Lewis or ABO (H) blood type, smoking, pregnancy, parturition, or phase of menstrual cycle. The use of the S‐Tn antigen as a tumor marker for various gynecologic cancers requires study.