Free PSA (f-PSA): A Prostate Marker

What is Free PSA

Free PSA (f-PSA) is the fraction of prostate-specific antigen (PSA) that circulates in the blood unbound to proteins. The total PSA value measures all prostate-specific antigen, while Free PSA shows what proportion remains free. This ratio is especially important when total PSA falls in the intermediate zone (4–10 ng/mL) and a more precise assessment of prostate cancer risk is needed.

The Free PSA percentage is calculated using the formula: (Free PSA / Total PSA) × 100. The higher the Free PSA percentage, the lower the likelihood that the change is related to cancer.

Reference Ranges

Free PSA values are not assessed in isolation but as a ratio to total PSA. Laboratories most commonly provide the following guidelines:

• Free PSA fraction above 25% — lower risk of prostate cancer.
• Free PSA fraction 15–25% — intermediate zone, additional evaluation needed.
• Free PSA fraction below 15% — higher probability of prostate cancer, biopsy worth considering.

These figures are indicative — the final decision is made by the physician, taking into account age, family history, and other tests.

Why Free PSA Percentage May Be Low

A low Free PSA percentage may be associated with prostate cancer, because cancer cells more often produce PSA that binds to blood proteins. However, this is not a definitive diagnosis — a low percentage only increases the probability and requires further investigation.

Other factors that can affect the Free PSA proportion: prostate inflammation (prostatitis), urinary tract infection, or recent procedures in the prostate area.

Why Free PSA Percentage May Be High

A high Free PSA percentage most often indicates benign prostatic hyperplasia (BPH) — a natural enlargement of the prostate that is common in older men. This does not mean the prostate is completely healthy, but the likelihood that the PSA rise is related to cancer is lower.

In rare cases, a high Free PSA percentage can also be observed with a normal total PSA, especially in younger men.

What to Do Next

If your Free PSA percentage is below 15%, your doctor may recommend additional tests: prostate MRT, repeat PSA after a few weeks, or a biopsy. It is important not to panic — a low percentage does not mean a diagnosis, but only a basis for further investigation.

If your Free PSA percentage is normal or high but you have urinary difficulties, get checked regularly for BPH.

Monitoring Over Time

A one-time PSA value is less informative than the trend over several months or years. QbiLabs allows you to track the dynamics of both total and Free PSA — a sudden change is more informative than a single value. Men aged 50 and over (or from 45 if there is a family history of prostate cancer) are recommended to be tested annually.

Questions for Your Doctor

1. What is my Free PSA percentage and do I need additional tests? 2. Is the change in PSA over the past year a cause for concern? 3. Do I need a prostate MRT or biopsy? 4. How often should I repeat the PSA test given my age and family history?

*This is not medical advice. Consult your doctor for health-related decisions.*