free prostate-specific antigen (free PSA) in serum/plasma
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Indications
- PSA > 4 ug/L (> 6 ug/L if 66-75 years of age)
- assess risk of prostate cancer
Clinical significance
- PSA is found in serum complexed with alpha 1-antichymotrypsin (> 85%) & in free form
- with total PSA 4-10 ng/mL,
- 95% of men with prostate cancer have free PSA < 25%,
- 20% of men with BPH have free PSA < 25%
Procedure
- two different antibodies used
- one detects PSA complexed to alpha-1 antichymotrypsin; the other detects only free PSA
- equilibrium dialysis is not useful since PSA is not easily dialyzed from PSA-apha-1 antichymotrypsin complex
Differential diagnosis
Management
- if %free PSA is < 25%, then refer patient to urology for prostate biopsy
- if patient is > 75 years, it is not necessary to order free PSA
- if patient is > 75 years & PSA is > 20 ug/L, refer to urology/oncology for androgen deprivation therapy
More general terms
Additional terms
References
- ↑ Catalona WJ, Partin AW, Slawin KM, Brawer MK, Flanigan RC, Patel A, Richie JP, deKernion JB, Walsh PC, Scardino PT, Lange PH, Subong EN, Parson RE, Gasior GH, Loveland KG, Southwick PC. Use of the percentage of free prostate-specific antigen to enhance differentiation of prostate cancer from benign prostatic disease: a prospective multicenter clinical trial. JAMA. 1998 May 20;279(19):1542-7. PMID: https://www.ncbi.nlm.nih.gov/pubmed/9605898
- ↑ Panel of 3 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0080206.jsp