Free to Total PSA Ratio (%fPSA)
Other marker
Free PSA Ratio
Free to Total PSA Ratio (%fPSA)
Free PSA expressed as a percentage of total PSA. Used to separate benign prostate enlargement from cancer when total PSA sits in the borderline range.
PED Notes
Its whole purpose is to add information when total PSA is equivocal, typically 4 to 10 ug/L, where an elevated result could be benign enlargement or could be cancer. Cancerous tissue produces proportionally more bound PSA, so a LOW ratio is the concerning direction, which is the opposite of how most markers on this site read. Roughly, above 25% is reassuring and below 10% carries substantially higher cancer risk. It matters here because androgens drive prostate growth and both testosterone therapy and long-term AAS use raise total PSA, so enhanced athletes hit that equivocal range more often and more often face an unnecessary biopsy decision. Note this ratio is only interpretable alongside total PSA: it is meaningless when total PSA is normal, and it does not replace urological assessment.
When low
Read the direction carefully: low is the concerning result here, unlike most markers.
Rough interpretation, and only when total PSA is in the equivocal 4 to 10 ug/L range:
- Above 25%: more consistent with benign prostatic hyperplasia
- 10 to 25%: intermediate, judged with age, prostate volume and PSA velocity
- Below 10%: substantially higher probability of prostate cancer, and a strong reason for urological referral
This is a referral marker, not a self-management one. A low ratio with a raised PSA warrants a urologist. Nothing on this page substitutes for that.
Before acting, rule out the things that distort PSA:
- Ejaculation within 48 hours, cycling, prostate examination, catheterisation, or recent prostatitis all raise PSA
- Free PSA is unstable in a sample left too long before separation, which can produce a falsely low ratio
- Repeat an abnormal result before making decisions
Context for enhanced athletes: testosterone therapy and AAS raise total PSA, which pushes more people into the equivocal band where this ratio gets ordered. That is expected, and a raised total PSA on TRT is not itself evidence of cancer. See PSA.
References:
- Catalona, W. J., Partin, A. W., Slawin, K. M., et al. (1998). Use of the percentage of free prostate-specific antigen to enhance differentiation of prostate cancer from benign prostatic disease. JAMA, 279(19), 1542-1547. DOI: 10.1001/jama.279.19.1542
- Roddam, A. W., Duffy, M. J., Hamdy, F. C., et al. (2005). Use of prostate-specific antigen isoforms for the detection of prostate cancer in men with a PSA level of 2-10 ng/ml: systematic review and meta-analysis. European Urology, 48(3), 386-399. DOI: 10.1016/j.eururo.2005.04.015
History Chart
Reading History
Frequently Asked Questions
Reference Ranges
Standard Range
Not available