[Initial basic and clinical evaluation of a solid-phase immunoradiometric assay for sialyl SSEA-1 antigen: 1. Evaluation of assay conditions and normal values].

We describe a solid-phase immunoradiometric sandwich assay method for a new tumor marker, sialyl SSEA-1 (sialyl LeX-i), using RIA kits (prepared by Otsuka Assay Laboratories). The assay required only duplicate 20-microliter samples, and the concentration of sialyl SSEA-1 antigen in serum was determined with reference to a standard curve ranging from 0 to 224 arbitrary unit/ml. The intra- and inter-assay reproducibilities and analytical recovery of antigen were excellent. The cut-off value (38 unit/ml) was obtained as mean + 2SD, which was calculated from the antigen concentration in sera from 1,105 healthy individuals. Also described are the alterations of normal values by age, sex, and Lewis blood group status.