Progesterone in diagnosis of ectopic pregnancy

Previous reports suggest that serum progesterone value may be useful in the diagnosis of ectopic pregnancy. These studies have based discriminatory thresholds on a limited number of patients without using statistical correction for biologic variability in an infinitely large population. This study was designed to determine the ability of a single progesterone value to discriminate between normal, ectopic and blighted pregnancies. Sera were obtained from all positive beta HCG tests at Shands Hospital, University of Florida. All samples were assayed simultaneously with a solid phase RIA for progesterone and the results compared with pregnancy outcome. The mean progesterone for normal pregnancies was 32.8 +/- 4.25 ng/ml (n = 49), for ectopic pregnancies 7.8 +/- 0.79 ng/ml (n = 51), and pregnancies which spontaneously aborted 8.1 +/- 0.91 ng/ml (n = 74). Using individual prediction limits progesterone greater than 24 ng/ml would exclude an ectopic pregnancy in 99% of patients. Thus, this test may be useful in selected patients when the diagnosis is unsure after beta HCG and transvaginal ultrasound have been performed.