Effect of serum lipids on radioimmunoassays of unconjugated estriol in serum.

Abstract

Abstract Controversy regarding the presence of a circadian rhythm in unconjugated estriol in serum during pregnancy led us to study the possibility that the observed rhythms actually are the result of partitioning of estriol into serum lipids when these increase postprandially. Addition of triglycerides to purified estriol standards significantly decreased (p less than 0.001) apparent estriol as detected by radioimmunoassay after separation on dextran-coated charcoal and significantly increased (p less than 0.001) estriol as detected by radioimmunoassay after double-antibody separation. Compensation for individual nonspecific binding of standards nullified the effect of lipids only in systems involving dextran-coated charcoal separation, incubated for 1.0 h at 37 degrees C followed by 1.0 h at 4 degrees C. In contrast to other protocols, data obtained with this system revealed no significant circadian variation in serum estriol concentrations in normal pregnant women (CV, 4.3%). Evidently, reported variations in apparent serum estriol concentration are artifactual.