Samples should be obtained before biopsy, prostatectomy or prostatic massage, since manipulation of the prostate gland may lead to elevated PSA levels persisting for up to 3 weeks.
Studies have shown conflicting results on the existence of an effect of digital rectal examination on PSA level. Therefore, when possible, obtain PSA samples before digital rectal examination.
PSA expression may be altered due to hormonal therapy for prostate cancer. Consequently, a low PSA result following a prostatic cancer treatment which includes hormonal therapy may not adequately reflect the presence of residual or recurrent disease.
Results may be affected if patient has developed Human Anti-Murine Antibodies (HAMA) due to exposure to murine based products
Heterophilic antibodies in human serum can react with the immunoglobulins included in the assay components causing interference with in vitro immunoassays. Samples from patients routinely exposed to animals or animal serum products can demonstrate this type of interference potentially causing an anomalous result.