Early diagnosis of ectopic pregnancy uses ultrasound with serial measurements of total human chorionic gonadotropin (hCG). The objective of this study was to explore the possibility that an isolated measurement of hCG isoforms/subunits rather than total hCG could be used as a single test for ectopic pregnancy. Methods: Total and intact hCG, free hCG ␤and ␣-subunits (hCG␤ and -␣), and hCG ␤-core fragment were measured by RIA and IRMA in the serum and urine of 76 women presenting at outpatient

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... rgency departments with a positive pregnancy test, lower abdominal pain, and/or vaginal bleeding. Final diagnoses were based on outcomes of pregnancies and tissue histology. Results: Twenty-seven of the 76 women were subsequently diagnosed with viable pregnancies, 37 with spontaneous miscarriage, and 12 with ectopic pregnancy. Concentrations of all forms of hCG were lower in cases of ectopic pregnancy and spontaneous miscarriage than in viable pregnancies. Serum samples gave better results than urine samples. The free hCG␤ isoform (P <0.0001) had 100% sensitivity at a specificity of 79% at a 281 pmol/L (6.5 g/L) cutoff. Total hCG (P ‫؍‬ 0.005) had comparable ROC characteristics with a 100% sensitivity and 68% specificity at a cutoff value of 1053 pmol/L (375 IU/L). Neither hCG␤ (P ‫؍‬ 0.7) nor total hCG (P ‫؍‬ 0.4) could distinguish ectopic pregnancies from spontaneous miscarriage. Conclusion: Measurement of serum free hCG␤ at the time of presentation can identify women with a high probability of ectopic pregnancy who may benefit from closer surveillance, reducing the risk of tubal rupture.