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Prostate-specific Antigen (PSA), Free:Total Ratio
- PSA, Free:Total Ratio
Measure the percentage of free (uncomplexed) PSA relative to the total amount of PSA in men with serum PSA concentrations between 4.0 and 10.0 ng/mL.
In this profile, free PSA is performed and percent free PSA is calculated, regardless of the concentration of total PSA. The interpretive guidelines provided for percent free PSA are based on a population of men with normal digital rectal exam (DRE) and total PSA between 4.0 and 10.0 ng/mL. Catalona and coworkers2 did not make specific recommendations regarding the use of percent free PSA for any other population of men.
Patients taking finasteride, an a-reductase inhibitor, will have diminished levels of PSA. PSA complexes are more stable than free PSA.1 The serum levels of both total and free PSA increase with prostate manipulation, but the free returns to premanipulation concentrations quicker. This can result in a transient elevation in percent free PSA.
Electrochemiluminescence immunoassay (ECLIA)
In general, serum PSA levels increase due to physical changes to prostate architecture caused by trauma, infection, inflammation, prostate manipulation, benign prostatic hypertrophy (BPH), or malignancy.3,4 The sensitivity of PSA levels to these changes serves as the basis for the clinical use of the test. The PSA concentration in the serum of healthy men is a millionfold lower than that in seminal fluid. PSA in seminal fluid is predominantly free or uncomplexed. In serum, the majority of PSA is bound to inhibitors, including α1-antichymotrypsin (ACT) and α2-macroglobulin (A2M). Measured total PSA consists of free and ACT-bound, since PSA complexed to A2M is not immunologically detectable.
Catalona and coworkers found that one in four patients with normal DRE and PSA levels between 4.0 and 10.0 ng/mL have prostate cancer.2 They recommend using a cutoff of 25% free PSA for this group of men (see Limitations) to identify individuals with an increased risk of prostate cancer. They found that 95% of men with cancer (as determined by biopsy) with normal DRE and total PSA between 4.0 and 10.0 ng/mL had percent free PSA of ≤25%. Their study further indicated that 20% of men with benign disease (as determined by biopsy) with normal DRE and a total PSA between 4.0 and 10.0 ng/mL had percent free PSA greater than the 25% cutoff.
Alternatively, percent free PSA may be used to determine the relative risk of prostate cancer in individual men.2 The following table lists the probability of prostate cancer for men with nonsuspicious DRE results and total PSA between 4.0 and 10.0 ng/mL, by patient age (see Limitations). See table.
% Free PSA
50 to 64 Years
65 to 75 Years
0.3 mL (Note: This volume does not allow for repeat testing.)
Red-top tube or gel-barrier tube
If a tube other than a gel-barrier tube is used, transfer separated serum to a plastic transport tube.
Maintain specimen at room temperature.1
Causes for Rejection
Citrated plasma specimen; improper labeling
Values obtained with different assay methods should not be used interchangeably in serial testing. It is recommended that only one assay method be used consistently to monitor each patient's course of therapy. This procedure does not provide serial monitoring; it is intended for one-time use only. For a complete test description, see Prostate-specific Antigen (PSA), Free:Total Ratio Reflex . If serial monitoring is required, please use the serial monitoring number 480780 to order.
This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
- 1. Woodrum D, French C, Shamel LB. Stability of free prostate-specific antigen in serum samples under a variety of sample collection and storage conditions. Urology. 1996 Dec; 48(6A Suppl):33-39.8973697
- 2. Catalona WJ, Partin AW, Slawin KM, et al. Use of 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):1542-1547.9605898
- 3. Sokoll LJ, Chan DW. Prostate-specific antigen. Its discovery and biochemical characteristics. Urol Clin North Am. 1997 May; 24(2): 253-259.9126221
- 4. Polascik TJ, Oesterling JE, Partin AW. Prostate-specific antigen: A decade of discovery--what we have learned and where we are going. J Urol. 1999 Aug; 162(2):293-306.10411025
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|480947||PSA Total+% Free||010334||Prostate Specific Ag, Serum||ng/mL||2857-1|
|480947||PSA Total+% Free||480782||PSA, Free||ng/mL||10886-0|
|480947||PSA Total+% Free||480799||% Free PSA||%||12841-3|