A direct radioimmunoassay for estriol-16alpha-glucosiduronate: its use in the determination of plasma and urine levels and renal clearance of this conjugate in pregnancy.

A direct radioimmunoassay which does not require hydrolysis or chromatography has been developed for estriol-16alpha-glucosiduronate in pregnancy plasma and urine. The antigen used in the development of this antiserum was prepared by joining the carboxylic acid group of estriol-16alpha-glucosiduronate covalently to the epsilon-amino group of the lysine residues in bovine serum albumin. Results indicate that the direct radioimmunoassay yields levels of estriol-16alpha-glucosiduronate in late pregnancy urine that are comparable to those obtained by mroe elaborate procedures involving chromatographic separation of the estriol conjugates, followed by enzymic hydrolysis and measurement of the freed estriol. In addition, good correlation was found between the total estrogen values in urine obtained by currently used chemical procedures and urinary levels of estriol-16alpha-glucosiduronate. The renal clearance of estriol-16alpha-glucosiduronate was determined in eight normal women during the third trimester, and the mean value +/- S.D. was 404 +/- 81 ml. per minute (range, 248 to 494). This method is suitable for the evaluation of variations in the plasma and urine levels of estriol-16alpha-glucosiduronate in pregnancy and offers significant advantages over the presently used chemical methods for monitoring fetal well-being.