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Phenothiazine compounds, which are known to produce false positive biological pregnancy tests, may also induce a false positive result in immunological tests for pregnancy.
Pathologists at Detroit General Hospital recently observed a false positive immunological test in an 82-year-old woman whose urine was used as a negative control in the hospital's laboratory.
The patient had been admitted for treatment of chlorpromazine-induced jaundice. She was receiving chlorpromazine (thorazine) for control of senile agitation.
Pregnancy tests of urine and serum became negative two weeks after the drug was withdrawn.
Reporting on the case to the annual meeting of the American Society of Clinical Pathologists, Frank Paoletti, MD, said the false positive result probably was caused by the excretory by-products of thorazine in the urine, or a thorazineinduced increase in gonadotrophins.
(Paul L. Wolf, MD, professor of pathology at Wayne State University and a co-author on the report, told The Journal that in
False Positive Pregnancy Tests and Phenothiazine. JAMA. 1966;198(1):A42. doi:10.1001/jama.1966.03110140018005