PSA, Free
The part of the PSA in your blood that is not attached to other proteins. It is read next to total PSA, not by itself.
AI-verified against cited sources. Awaiting expert reviewAlso called fPSA, free PSALOINC 10886-0
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What it is
PSA (prostate-specific antigen) is a protein made by the prostate. In the blood, most PSA is attached to other proteins, and a smaller part floats free. This test measures the free part. Labs usually run it together with a total PSA test and then divide free by total to get the percent free PSA, which is reported as its own result. Free PSA is rarely ordered alone.
Why it matters
On its own, the free PSA number says little, because it goes up and down with total PSA. Its value comes from the percentage of PSA that is free. In men whose total PSA is mildly raised, a lower percent free PSA goes along with a higher chance that a biopsy will find prostate cancer, and a higher percent goes along with a lower chance. Clinicians can use that to help decide whether to look further. It is an extra clue, not a diagnosis. The AUA guideline says clinicians may use add-on tests like this when the extra information would change the decision about a biopsy, and calls percent free PSA perhaps the most widely available one.
If it’s high
A higher free PSA usually just reflects a higher total PSA. Anything that releases more PSA into the blood can raise both, so the free PSA number alone does not point to a cause. Your clinician looks at the percent free PSA and at your total PSA trend instead.
Common causes
- An enlarged prostate (benign prostatic hyperplasia)
- Prostate inflammation or infection (prostatitis)
- A recent prostate biopsy or other procedure
- Prostate cancer
What can help
- Ask your clinician how your free PSA fits with your total PSA and your percent free PSA
- Ask whether to repeat the test in a few weeks to a few months, since many raised results settle
- Tell your clinician about recent infections, urinary symptoms, procedures and any medicines you take
What can affect your result
- Total PSA: free PSA rises and falls with it
- Prostate enlargement, inflammation or infection
- A recent prostate biopsy, catheter or other procedure (Mayo suggests waiting about 6 weeks after a needle biopsy)
- A rectal exam: Mayo advises drawing blood first because it may cause a short rise, while the AUA guideline found little effect on total PSA
- 5-alpha-reductase inhibitor medicines (such as finasteride), which lower PSA and free PSA
- The test maker: Roche and Beckman results differ and should not be mixed
- Biotin supplements, which can affect some assays but not others
- How quickly the blood is processed after the draw
- A prostate biopsy, catheter or other prostate procedure can raise PSA results for weeks. Mayo Clinic Laboratories recommends waiting about 6 weeks after a needle biopsy, and drawing blood before a rectal exam, which may cause a short-lived rise in some assays.
- 5-alpha-reductase inhibitor medicines (such as finasteride) lower PSA and free PSA.
- Biotin supplements: on the Beckman Access assay free PSA can read falsely low, and Mayo asks that high-dose biotin (over 5 mg a day) be paused for at least 8 hours before the draw. Mayo says biotin up to 1,200 ng/mL does not interfere with its Roche total and free PSA assays.
- Rare antibodies (human anti-mouse or heterophile antibodies, or antibodies to streptavidin or ruthenium) can cause false results on some immunoassays.
- Free PSA must be handled promptly: ARUP asks for serum to be separated within 2 hours and Mayo within 3 hours, then frozen or refrigerated.
- Assays from different makers (for example Roche and Beckman) give different numbers and are not interchangeable. Use the same lab and method for repeat tests.
A temporary rise from a procedure or infection fades over weeks. Mayo recommends waiting about 6 weeks after a needle biopsy before testing.
When to talk to a clinician
Free PSA has no cutoff of its own. Talk with your clinician soon if your total PSA is above your lab's range or keeps rising, or if you have blood in your urine or semen, trouble passing urine, or new pain in your hips, back or pelvis. Get urgent care if you cannot pass urine, or if you have fever and chills with painful urination.
Questions you could ask
- Could any medicine, supplement or recent procedure have changed my PSA results?
- Should my PSA tests always be done at the same lab?
- Should we look at my percent free PSA together with my total PSA?
- Would repeating the test in a few weeks or months help?
- Would another test, such as a phi score or an MRI, add useful information in my case?
Questions people ask
Is there a normal range for free PSA?
Not on its own. ARUP lists its reference interval as 'by report,' and labs do not publish a cutoff for the free PSA number alone. It is read as a percentage of total PSA, which is its own result.
Why was free PSA ordered along with my total PSA?
Usually because total PSA was in a middle range, where it is hard to tell from the total alone whether more testing is needed. Mayo runs the ratio when total PSA is 4.0 to 10.0 ng/mL, and the AUA guideline says add-on tests are typically used for total PSA of about 2.5 to 10 ng/mL.
Show the science and sources
Units
- 1 ng/mL = 1 ng/mL
- 1 ng/mL = 1 µg/L
Is a change real?
Free PSA naturally varies about 7.1% from test to test in the same healthy person. Between two results from the same lab, a rise of 25% or more, or a fall of 20% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Critical review and meta-analysis of biological variation estimates for tumor markers (Marques-Garcia F et al., EFLM WG-BV).
For clinicians and researchers
In serum, PSA (KLK3) is mostly bound to alpha-1-antichymotrypsin, with a smaller unbound free fraction; PSA enveloped by alpha-2-macroglobulin is not detected by immunoassays (Mayo). Free PSA is measured by two-site immunoassays: Mayo's total and free PSA test uses the Roche Elecsys assays (total PSA standardized to WHO 96/670 and free PSA to WHO 96/668), and its phi test uses the Beckman Access Hybritech assays. Free PSA has no stand-alone reference interval; ARUP lists the reference as 'by report'. It is interpreted as the free-to-total ratio (see percent free PSA), where lower percentages are linked to a higher chance of finding cancer on biopsy when total PSA is mildly raised. The adjunct tests are typically used for a total PSA of about 2.5 to 10 ng/mL (AUA); Mayo reports the ratio only for total PSA 4.0 to 10.0 ng/mL and ARUP's text describes use from 3 to 10 ng/mL. Both labs state that values from different methods are not interchangeable, and a study of phi noted that results apply to the specific Beckman assays used and differ with other manufacturers. Pre-analytics matter: ARUP asks for serum or plasma to be separated within 2 hours, Mayo within 3 hours, and a phi validation study processed samples within 8 hours and froze them. ng/mL and µg/L are numerically identical, and labs normally report free PSA in mass units.
LOINC 10886-0 (primary), 83113-1. Specimen: serum-or-plasma.
Sources
- Prostate Specific Antigen, Free Percentage (Includes Free PSA and Total PSA) (test 0080206), ARUP Laboratories
- PSAFT - Overview: Prostate-Specific Antigen (PSA), Total and Free, Serum, Mayo Clinic Laboratories
- P2PHI - Overview: [-2]Pro Prostate Specific Antigen with Prostate Health Index, Serum, Mayo Clinic Laboratories
- Early Detection of Prostate Cancer: AUA/SUO Guideline (2023, amended 2026), American Urological Association (2026)
- A multicenter study of [-2]pro-prostate specific antigen combined with prostate specific antigen and free prostate specific antigen for prostate cancer detection in the 2.0 to 10.0 ng/ml prostate specific antigen range, The Journal of Urology (2011)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.