Radioimmunoassay for norethindrone. II. Plasma levels in hypertensive and normotensive oral contraceptive users

A sensitive radioimmunoassay for measurement of norethindrone (N) in blood plasma has been developed. The coefficient of variation within the assay and between assays was 7 and 13.5 percent respectively. The procedural blanks were negligible, and recovery was approximately 81.8 percent. Blood plasma levels of N in 20 normotensive and 6 hypertensive women who were ingesting oral contraceptives (OCs) were measured, and the results indicate that the subjects who became hypertensive while taking OCs had significantly higher levels of N compared with normotensive OC users (p less than 0.001)