Discordant human chorionic gonadotropin results: causes and solutions.

This study was performed to demonstrate the phenomenon of discordant human chorionic gonadotropin (hCG) results, in which some serum specimens are positive in one hCG detection procedure but negative in another procedure. Nine different quantitative hCG procedures were used to document discordant hCG results in 22 cases. A two-site monoclonal antibody immunoradiometric assay had the least tendency to give aberrant low-positive hCG values in nonpregnant patients without neoplasms. Potential causes of discordant hCG results are discussed, and guidelines for dealing with them are suggested. Recommended approaches include analysis in an alternate hCG detection procedure that uses a different technology for collection of antigen-antibody complex, dilution analysis, and sequential hCG analysis.