Editing Prostate-specific antigen (section)

===Free PSA===

[[Image:Free PSA bar graph.svg|thumb|300px|Risk of prostate cancer in two age groups based on ''Free PSA'' as % of Total PSA<ref>{{cite journal | vauthors = 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 | title = Use of the percentage of free prostate-specific antigen to enhance differentiation of prostate cancer from benign prostatic disease: a prospective multicenter clinical trial | journal = JAMA | volume = 279 | issue = 19 | pages = 1542–1547 | date = May 1998 | pmid = 9605898 | doi = 10.1001/jama.279.19.1542 }}</ref>]]
Most PSA in the blood is bound to serum proteins. A small amount is not protein-bound and is called 'free PSA'. In men with prostate cancer, the ratio of free (unbound) PSA to total PSA is decreased. The risk of cancer increases if the free to total ratio is less than 25%. (See graph) The lower the ratio is, the greater the probability of prostate cancer. Measuring the ratio of free to total PSA appears to be particularly promising for eliminating unnecessary [[Biopsy|biopsies]] in men with PSA levels between 4 and 10{{nbsp}}ng/mL.<ref>{{cite journal | vauthors = Catalona WJ, Smith DS, Ornstein DK | title = Prostate cancer detection in men with serum PSA concentrations of 2.6 to 4.0 ng/mL and benign prostate examination. Enhancement of specificity with free PSA measurements | journal = JAMA | volume = 277 | issue = 18 | pages = 1452–1455 | date = May 1997 | pmid = 9145717 | doi = 10.1001/jama.277.18.1452 }}</ref> However, both total and free PSA increase immediately after ejaculation, returning slowly to baseline levels within 24 hours.<ref name="Herschman-1997"/>