Prostate-specific Antigen (PSA), Free:Total Ratio

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CPT Code:

84153, 84154

Test Type: 0.8 mL Serum
Stability Time:
Temperature Period
Freeze 14 days
Room 3 days  
Refrigerator 3 days  
Freeze/thaw cycles Stable x3


Measure the percentage of free (uncomplexed) PSA relative to the total amount of PSA in men with serum PSA concentrations between 4.0-10.0 ng/mL. 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.[2,3] 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 alpha 1-antichymotrypsin (ACT) and alpha-2-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.[4] They recommended 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 the men with cancer (as determined by biopsy) with normal DRE and total PSA between 4 and 10 ng/mL had percent free PSA <=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 and 10 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.[4]

In this panel, 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 coworkers[4] did not make specific recommendations regarding the use of percent free PSA for any other population of men. Patients taking finasteride, an alpha-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.

Collection Details:

Collection Instructions:

Values obtained with different assays should not be used interchangeably in serial testing. It is recommended that only one assay method be used consistently to monitor a patient's course of therapy. This procedure does not provideserial monitoring; it is intended for one-time use only. For a complete test description, see Prostate-specific Antigen (PSA), Free:Total Ratio Reflex (480772). 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 doseof 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.

Red-top tube or gel-barrier tub.

If tube other than gel-barrier tube is used, transfer separated serum to a plastic transport tube.

Maintain specimen at room temperature.