Serum heterophile antibodies interfere with prostate specific antigen test and result in over treatment in a patient with prostate cancer.

PURPOSE: We evaluated how naturally occurring heterophile antibodies in patient serum interfered with prostate specific antigen (PSA) immunoassay, resulting in over treatment for prostate cancer.
MATERIALS AND METHODS: Serum samples were treated with heterophilic blocking reagent (Scantibodies Laboratory, Inc., Santee, California). Treated and untreated samples were tested by the Medics (Tosoh, Foster City, California ) Tandem-R (Beckman-Coulter Inc., Chaska, Minnesota) and Elecsys (Roche Molecular Biochemical, Indianapolis, Indiana) PSA assays. Heterophile antibodies were measured directly in treated and untreated samples by the human anti-mouse antibody immunoradiometric assay and heterophilic antibody identification enzyme immunoassay (Scantibodies Laboratories, Inc.).
RESULTS: Human anti-mouse Ig heterophile antibodies in patient serum caused false-positive PSA test findings after radical prostatectomy, resulting in over treatment for presumed disease recurrence.
CONCLUSIONS: If PSA is detectable after radical prostatectomy and the likelihood of incomplete resection or systemic disease is low, the presence of heterophile antibodies should be considered.