PROSTATE SPECIFIC ANTIGEN (PSA) - serum

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Specimen: 5 mL blood in plain tube.

Method: Immunoassay.

Reference Interval: Depends on method and varies with age; consult pathologist.

Application: Diagnosis and monitoring of prostatic carcinoma. PSA has generally replaced acid phosphatase, as it has greater sensitivity (esp for early invasive carcinoma) and specificity. The test is not recommended as a stand-alone screening test for carcinoma of the prostate.

Interpretation: The result should always be interpreted in conjunction with the findings on digital rectal examination and other clinical findings. Marked elevation is indicative of carcinoma, but normal or slightly elevated PSA levels do not exclude it. The most common non-malignant cause of increased PSA is benign prostatic hypertrophy, however levels are also increased in prostatitis, prostatic ischaemia and/or infarction and acute renal failure. Assays for total PSA should measure the free and complexed forms equally. Specific assays are also available for each form, as it is suggested that the complexed form is more specific for prostatic cancer. The diagnostic role of complexed PSA assay is not yet established. Results that do not correspond to the clinical findings should be repeated on a fresh collection. PSA is particularly useful in monitoring the course of prostatic carcinoma.

Reference: Nash AF and Meleginek I. Endocr Relat Cancer 2000; 7: 37-51.

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