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Medical Science Monitor Basic Research


Falsely Undetectable Prostate-Specific Antigen (PSA) Due to Presence of an Inhibitory Serum Factor: A Case Report and Review of Pertinent Literature

Unusual clinical course, Mistake in diagnosis, Clinical situation which can not be reproduced for ethical reasons

Nicholas B. Loudas, Anthony A. Killeen, Vikram Palamalai, Christopher J. Weight, Arpit Rao, L. Chinsoo Cho

USA Department of Radiation Oncology, University of Minnesota Medical Center, Minneapolis, MN, USA

Am J Case Rep 2019; 20:1248-1252

DOI: 10.12659/AJCR.917137

Available online:

Published: 2019-08-24

BACKGROUND: Few cases of falsely undetectable PSA due to the presence of an inhibitory serum factor have been reported in the world literature. We present a case of falsely low-to-undetectable PSA with data from a serum dilution series, the current literature on biochemical assay interference, and the implications for prostate cancer salvage treatment.
CASE REPORT: A 63-year-old man was treated with prostatectomy for high-risk prostate cancer and was found to have a rising PSA after approximately 3 years following surgery. He subsequently transferred his care to a different health system and was found to have an undetectable PSA. He was eventually found to have an elevated PSA once again after the particular assay at this institution was changed. He thus received salvage prostate radiotherapy and androgen deprivation therapy.
CONCLUSIONS: While falsely low PSA results cannot be explained by the presence of serum heterophile antibodies, competitive antibody interference against the immunoassay reagents or anti-PSA antibodies are possible explanations for the results of the dilution experiments performed in this case study. We suggest that unexpected PSA testing results should raise concern for assay interference and warrant further clinical workup.

Keywords: Antibodies, Blocking, Immunoenzyme Techniques, Prostate-Specific Antigen, Prostatic Neoplasms