A sensitive hemagglutination assay of human chorionic gonadotropin in the diagnosis of ectopic pregnancy.

Hemagglutination assay of human chorionic gonadotropin (hCG) in the urine of patients suspected of having ectopic pregnancies has proved to be a highly sensitive method of detecting the condition. Moreover, the technique is simple and inexpensive. Hemagglutination assays were used in 167 patients with a diagnosis of ectopic pregnancy and in screening 415 patients in whom there was a possibility of ectopic pregnancy. In the former group, hCG titers in urine of more than 500 IU/liter were detected in 136 patients: among the remaining 31, the pregnancies were clinically old and resolving in 22. Low hCG titers were associated with a significantly shorter period of amenorrhea and a protracted clinical course. In the second group, a false-positive rate of 1.7% occurred when the sensitivity of the assay was limited. Increasing the sensitivity of the assay to avoid false-negative results, though also increasing the false-positive rate, would help to reduce the number of cases in which more complex isotope assays are required.