Reliability of progesterone measurements in urine

A radioimmunoassay (RIA) of progesterone in urine is described. After the addition of labelled progesterone, morning urine was extracted with n-hexane adn the residue was either directly subjected to RIA, or chromatographed on celite prior to RIA. The progesterone from celite chromatography was radiochemically pure. RIA after chromatography was therefore considered valid. The non-chromatographed procedure resulted in overestimations, the degree of which was inversely proportional to progesterone content. The results obtained by the two procedures were well correlated (r = 0.88 and 0.93, for 2 different groups of samples.