Pitfall in the diagnosis of ectopic pregnancy: immunocytochemical evaluation in a patient with false-negative serum beta-hCG levels.

Tubal pregnancy specimens from a patient with undetectable serum beta-hCG levels and a control case with a low beta-hCG titer by radioimmunoassay were analyzed using peroxidase-antiperoxidase immunocytochemical localization of placental proteins. The results indicated that deficient production of beta-hCG by ectopic trophoblast was responsible for false-negative pregnancy tests in one patient.