Removal of Substances Interfering with the Rapid Assay of Estrogen in Pregnancy Urine1

Abstract

Substances interfering with the rapid assay of estrogens in pregnancy urine are largely eliminated when the estrogens are first precipitated from the urine with 70% (w/v) (NH₄)₂SO₄. This is true for both the shortened estriol and the Ittrich total estrogen estimations. A 10-fold dilution of the urine prior to acid hydrolysis, which overcomes a marked reduction of the estrogen assay value following acid hydrolysis of undiluted diabetic urine, is usually made unnecessary when assays are carried out on solutions of the (NH₄)₂SO₄ precipitate of the urine. In fact, a higher assay value is frequently obtained for the precipitate than for the urine from which the precipitate was prepared, when both are assayed by the dilution-acid hydrolysis technique. The precipitate can also be assayed by the Ittrich procedure or a modification thereof, even when the urine contains substances which interfere with the successful application of the procedure to the urine itself. The interfering substances in both types of rapid assay are apparently not precipitated from the urine with the estrogens by (NH₄)₂SO₄ and are discarded with the supernatant. The direct assay by an Ittrich (or a modified Ittrich) technique usually gives an even higher assay value than the dilution acid hydrolysis technique when both are applied to the precipitate. This may be due either to the presence in the urine of additional substances which interfere with assays conducted by the acid hydrolysis technique and which are precipitated with the estrogen by the (NH₄)₂SO₄ or to a destruction of acid labile estrogens or to both.