PSA, Free Percent (% Free PSA)
The share of your PSA that is not attached to other proteins. With a mildly raised total PSA, a lower share goes with a higher chance a biopsy finds cancer.
AI-verified against cited sources. Awaiting expert reviewAlso called %fPSA, %FPSA, f/t PSALOINC 12841-3
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What it is
PSA in your blood comes in two main forms: attached to other proteins (bound) and floating free. Percent free PSA is the free part divided by total PSA, times 100. Labs calculate it for you when both tests run on the same blood sample. Some labs print it as a ratio such as 0.15 instead of 15%. It is not a stand-alone test for cancer. It is meant for men 50 and older whose total PSA is mildly raised (Mayo reports it for total PSA of 4.0 to 10.0 ng/mL) and whose rectal exam was not suspicious.
Why it matters
When total PSA is only mildly raised, there are many possible causes besides cancer, and a biopsy often finds nothing. Percent free PSA gives an extra clue. A lower percentage goes with a higher chance that a biopsy will find prostate cancer, and a higher percentage goes with a lower chance. In Mayo's table, cancer was found in 56 of 100 men whose percent free PSA was 10% or lower, and in 8 of 100 men whose percent was over 25%. Your clinician may use it to help decide between watching, an MRI or a biopsy. It does not diagnose cancer. The AUA guideline calls percent free PSA perhaps the most widely available add-on test.
If it’s low
A lower percent free PSA goes with a higher chance that a biopsy will find prostate cancer. The lower the percentage, the higher the chance: in Mayo's table, cancer was found in about 56 of 100 men at 10% or lower, so about 44 of 100 had none found. A low percentage does not mean you have cancer.
Common causes
- A noncancerous prostate condition, since many men with a low percentage have no cancer found on biopsy
- Prostate cancer
What can help
- Ask your clinician what the percentage means for you, given your age, total PSA and exam
- Ask whether a repeat PSA, an MRI or another test such as a phi score would help decide next steps
- Use the same lab for repeat tests, since assays differ
If it’s high
A higher percent free PSA (over 25%) goes with a lower chance that a biopsy will find prostate cancer. In Mayo's table, about 8 of 100 men in this group had cancer found. That is lower, but it does not rule cancer out.
Common causes
- A noncancerous prostate condition, such as an enlarged prostate, behind the raised total PSA
- Prostate cancer is still possible, at a lower chance
What can help
- Ask your clinician how the percentage fits with your total PSA trend, family history and exam
- Ask when to repeat PSA testing
What can affect your result
- The test maker: Roche and Beckman results and probability tables differ and should not be mixed
- Total PSA: the percentage is most useful when total PSA is mildly raised (about 4 to 10 ng/mL, or 2.5 to 10 in some uses)
- Age: Roche-based tables give different probabilities for ages 50–59, 60–69 and 70 and older
- A recent prostate biopsy, catheter, infection or other procedure
- 5-alpha-reductase inhibitor medicines, which lower PSA and free PSA
- Biotin supplements, which affect some assays but not others
- How quickly the blood is processed after the draw
- Anything that affects total PSA or free PSA affects the percentage: a recent prostate biopsy or procedure, a urinary or prostate infection, and 5-alpha-reductase inhibitor medicines. Mayo recommends waiting about 6 weeks after a needle biopsy.
- Mayo advises drawing blood before a rectal exam because it may cause a short rise in some assays. The AUA guideline found no appreciable change in total PSA.
- Biotin supplements can falsely lower free PSA on the Beckman Access assay (Mayo asks that doses 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 assays.
- Free PSA needs prompt handling: ARUP asks for serum to be separated within 2 hours and Mayo within 3 hours.
- Roche and Beckman assays give different results, and the probability tables differ between them. Do not mix assays when comparing results over time.
- Many labs report the percentage only when total PSA is in a middle range (Mayo: 4.0 to 10.0 ng/mL), so it may be missing from your report.
A temporary rise from a procedure or infection fades over weeks, so the percentage can shift during that time.
When to talk to a clinician
Talk with your clinician about next steps if your percent free PSA is 25% or lower and your total PSA is between 4 and 10 ng/mL. A 25% cutoff was proposed in a 1998 trial of 773 men, in which it found 95% of cancers while avoiding 20% of unnecessary biopsies. Talk with your clinician soon about 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
- Which assay does my lab use, and should I use the same lab for repeat tests?
- How does my percent free PSA fit with my total PSA and my other results?
- When should we repeat my PSA tests?
- What does my percent free PSA mean for next steps, such as a repeat test, an MRI or a biopsy?
- Would another test, such as a phi score, help in my case?
- Could a recent procedure, infection or medicine have changed this result?
Questions people ask
Why does my report show 0.15 instead of 15%?
Some labs print the free-to-total result as a ratio (0.15) and others as a percentage (15%). They mean the same thing. Multiply the ratio by 100 to get the percentage.
Why do different labs use different cutoffs?
The tables come from studies that used particular assays. Roche-based tables (ARUP, and Mayo's total and free PSA test) use groups of 10%, 18% and 25% and vary by age. Beckman-based tables (Mayo's phi test) use groups of 10%, 15%, 20% and 25%. They are not interchangeable, so it helps to ask which assay your lab used.
Why was my percent free PSA not calculated?
Many labs calculate it only when total PSA is in a middle range. Mayo, for example, reports it only when total PSA is 4.0 to 10.0 ng/mL, because the numbers have been studied mostly in that range. Your clinician can tell you whether it is worth adding.
Show the science and sources
Units
- 1 % = 1 %
- 1 % = 0.01 ratio (0–1)
Open the % Free PSA unit converter
Is a change real?
% Free PSA naturally varies about 5.3% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 16% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.
For clinicians and researchers
Percent free PSA is free PSA divided by total PSA (LOINC 12841-3). Mayo's Roche-based test reports the free:total ratio (for example 0.18), while its Beckman-based phi test reports % free PSA; ARUP reports a whole-number percent. Only the Beckman table (Mayo P2PHI) uses five groups (10%, 15%, 20%, 25%); the Roche tables (ARUP and Mayo PSAFT) use four groups (10%, 18%, 25%) and vary by age, with probabilities of 49%, 27%, 18% and 9% at ages 50–59, 58%, 34%, 24% and 12% at 60–69, and 65%, 41%, 30% and 16% at 70 and older. The 8% to 56% span of the Beckman table matches the Hybritech Tandem assay trial of 773 men aged 50 to 75 with total PSA 4.0 to 10.0 ng/mL and a benign rectal exam (Catalona 1998), in which a 25% cutoff kept 95% sensitivity, and cancers found above 25% free were more common in older men and less aggressive. A negative biopsy does not rule out cancer: Mayo notes that up to 20% of men with a negative biopsy are later found to have cancer. In AUA terms, adjunct markers may be used when extra risk information would change the decision about biopsy (conditional recommendation, Grade C) and are typically applied to a PSA of about 2.5 to 10 ng/mL. In AUA's summary, removing percent free PSA from the 4Kscore model lowered its AUC from 0.821 to 0.699, and percent free PSA improved prediction of grade group 2 or higher cancer over total PSA (AUC 0.661 versus 0.551) in the phi study. Total PSA and free PSA must be measured on the same sample, and mixing makers' assays is not valid. Band boundaries are set 0.01 above each printed upper limit (for example 10.01) so that results of exactly 10%, 18% or 25% fall in the labs' lower group. The labs' tables are written for whole-number results, so a result with decimals, such as 10.5%, sits between two printed groups; ask your lab which group it uses. The Roche age-specific sets are listed first because both ARUP's and Mayo's total and free PSA tests use Roche assays; the Beckman set applies only if your lab used the Beckman assay.
LOINC 12841-3 (primary), 72576-2. Specimen: calculated.
Sources
- P2PHI - Overview: [-2]Pro Prostate Specific Antigen with Prostate Health Index, Serum, Mayo Clinic Laboratories
- 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)
- 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
- Early Detection of Prostate Cancer: AUA/SUO Guideline (2023, amended 2026), American Urological Association (2026)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.