Modification of the choriogonadotropin beta-subunit radioimmunoassay for determination of urinary choriogonadotropin

Abstract

The choriogonadotropin beta-subunit radioimminoassay has been used extensively to measure human choriogonadotropin in the sera of pregnant women and individuals with trophoblastic and nontrophoblastic tumors. Unmodified, this method cannot be used to measure choriogonadotropin in urine because of interfering substances. We circumvented the non-parallelism between the standards and serial dilutions of urine containing choriogonadotropin by adding pooled urine from men to the standard tubes and limiting the volume of urine to 100 microliter. This modified assay has a sensitivity of 3 int. units/liter of urine and is specific for choriogonadotropin concentrations of 40 int. units/liter of urine. Analytical recovery of choriogonadotropin added to urine ranged from 96 to 105%. The within-assay CV was 7.6%; the between-assay CV was 11.8%. Concentrations of choriogonadotropin in concurrently collected serum and urine samples from pregnant women correlated well. The test can be performed within 24 h by using the double-antibody method for separating bound from free hormone, or in 3 h with a dioxane method. The assay is about 20-fold more sensitive than the 2-min or 2-h slide and tube pregnancy tests, and seven-to 12-fold more sensitive than the radioreceptor assay.