Use of serum FSH to identify perimenopausal women with pituitary hCG.

BACKGROUND: Human chorionic gonadotropin (hCG) tests are performed on many female patients before performing medical procedures or administering medications that may harm a fetus. hCG of pituitary origin has been shown to increase with age. Therefore, mild increases in serum hCG in an older patient can be of pituitary origin and does not necessarily indicate pregnancy. The inability to rule out pregnancy in perimenopausal women can create clinical confusion and may delay needed therapies. Our objective was to determine the diagnostic utility of serum follicle-stimulating hormone (FSH) concentrations to rule out hCG of placental origin in perimenopausal women with a low concentration of serum hCG (5.0-14.0 IU/L). METHODS: Seven testing centers performed 39 742 physician-ordered serum quantitative hCG tests over a 15-month period. From these, 100 samples from women 41-55 years of age with serum hCG concentrations 5-14 IU/L were identified. We performed FSH testing and patient chart review for each sample. RESULTS: Twenty-three patients were found to have hCG of placental origin (pregnancy, resolving abortion, or gestational trophoblastic disease), and in those cases serum FSH was 0.4-43.8 IU/L. An FSH cutoff of 45.0 IU/L identified hCG of placental origin with 100% sensitivity and 75% specificity. FSH >45 IU/L was never observed when hCG was of placental origin (negative predictive value). CONCLUSIONS: These data indicate that quantitative serum FSH can be used to rule out pregnancy and hCG of placental origin in women 41-55 years of age with mild increase in serum hCG concentrations.