Assessment of corpus luteum function by direct radioimmunoassay for progesterone in blood spotted on filter paper.

In this specific, direct RIA for progesterone in capillary blood dried on filter paper, progesterone is eluted, with phosphate buffer containing bovine serum albumin, from 5.9 microL of blood dried on 5.0-mm (diameter) discs of filter paper. The eluate is assayed, with 125I-labeled progesterone-11 alpha-glucuronyl-tyramine as tracer, with separation by a double-antibody solid-phase technique. The sensitivity of the assay is 4.7 pg per tube, corresponding to 2.5 nmol per liter of blood. Within- and between-batch CVs averaged 7.0 and 9.2%, respectively, over the working range of the assay (4.5-64 nmol/L). Concentrations of progesterone in blood spots (y) correlated well with those in serum (x) as measured by an established direct RIA (Clin Chem 28:1314, 1982): y = 0.430x - 2.44 (r = 0.972, n = 104). Progesterone is stable in the blood spots for at least 15 weeks at 25 degrees C. The convenience of multiple sampling of blood by finger prick and the simplicity of the assay make this approach useful in investigating serial progesterone concentrations in outpatients.