An enzyme-linked immunosorbent assay for fetal steroid binding protein of human serum

The binding characteristics and quantitation of the recently reported fetal steroid binding protein (FSBP) cannot be determined on unpurified samples; an immunoassay was therefore desirable. The protein was purified to homogeneity in order to raise a highly specific polyclonal antibody. An enzyme-linked immunosorbent assay applicable to unpurified samples was developed. Intra- and inter-assay coefficients of variation are 8.0% and 9.2% respectively; there is a sensitivity of 30 fmol FSBP per well, and there is no cross-reactivity with other binding proteins. Results obtained with the assay correlate with the more complex ligand binding assay (r = 0.85; p less than 0.02). Measurement of sera showed that FSBP levels are higher in women than in men (51.2 +/- 10.62 nM; 41.2 +/- 13.65 respectively; p less than 0.05) and are elevated in cirrhotic women (66.4 +/- 18.67; p less than 0.05) and in males with hepatocellular carcinoma (62.2 +/- 13.05; p less than 0.002). Use of the enzyme-linked immunosorbent assay confirmed the identity of FSBP separate from sex hormone binding globulin.