fPSA

Free PSA (fPSA) is the portion of prostate-specific antigen (PSA) not bound to other blood proteins. It is always measured alongside total PSA from the same sample, with their ratio important for interpretation. The ratio helps a doctor assess whether moderately raised PSA needs further investigation.

Who the test is for

• men with moderately raised total PSA, most often between 4 and 10 µg/L;
• men with PSA from 2 µg/L because some laboratories and guidelines also use the ratio in this range;
• men with persistently borderline PSA whose previous investigation has not shown cancer;
• men whose doctor is deciding whether moderately raised PSA needs further investigation, for example repeat testing or urology referral.

What free PSA is and what it shows

PSA is a protein produced by prostate cells. Most is bound to other blood proteins, with a smaller portion circulating free. In prostate cancer, the free proportion is on average smaller than in benign prostate enlargement (benign hyperplasia).

Values nevertheless overlap between these conditions. The ratio therefore neither diagnoses nor excludes cancer but adds information for deciding the next step, such as monitoring or urology referral. fPSA alone without total PSA from the same sample is not useful.

The range between 4 and 10 µg/L is called the “grey zone” because cancer and benign enlargement often cannot be distinguished within it. With clearly high PSA the ratio changes little because a doctor recommends further investigation anyway. Whether PSA testing is needed at all is decided with a doctor because PSA alone is not a reliable screening test.

Save with a panel

Test fPSA is also included in this panel.

Prostate health panelPSA, fPSA, Urine: dipstick and sedimentPrice of individual tests: 50.00€45.00€ Original price was: 45.00€.31.50€Current price is: 31.50€.Details ›

All panels including fPSA (2) ›

Preparation and sample

Blood is taken from a vein and fasting is unnecessary. Preparation is the same as for PSA:

• avoid ejaculation and strenuous exercise, particularly cycling, for 48 hours before collection;
• collect blood before digital rectal prostate examination or at least a week afterwards;
• after prostate biopsy or surgery wait at least 6 weeks unless a urologist specifies otherwise;
• postpone testing until prostatitis or urinary tract infection resolves;
• tell your doctor about finasteride or dutasteride, which lower PSA by about half.

How to interpret the fPSA/PSA ratio

The ratio shows the percentage of total PSA that is free; a doctor calculates and interprets it from total and free PSA results. For example, with total PSA 6 µg/L and free PSA 0,9 µg/L, the ratio is 15 %. A lower free proportion means a higher likelihood of prostate cancer. As a guide:

• above around 25 %: more often supports benign enlargement;
• between around 10 and 25 %: an indeterminate range; decisions depend on other information;
• below around 10 %: a higher cancer likelihood, so a doctor usually recommends further investigation.

These thresholds are approximate, method-dependent and not absolute. Prostate size also affects the ratio because a large benign gland often gives a higher free fraction. A doctor interprets results alongside age, prostate examination, PSA trends and, if needed, prostate magnetic resonance imaging (MRI). Only biopsy diagnoses cancer.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the service price list. Total and free PSA and urinalysis are performed together in this panel: Prostate health.

Frequently asked questions

What does low free PSA mean?

A low free proportion, particularly below around 10 %, with raised total PSA increases prostate cancer likelihood but does not establish it. A doctor refers to a urologist, who decides on MRI and biopsy.

Is high free PSA a good sign?

A high free proportion, above around 25 %, more often accompanies benign enlargement. Cancer is not excluded, so a doctor continues monitoring PSA trends.

What if total PSA is normal but the ratio low?

The ratio has been validated primarily for moderately raised total PSA. With normal PSA, a low ratio alone has limited value, so a doctor interprets it alongside age, examination and earlier results.

Can I measure free PSA alone?

No. Free PSA is useful only with total PSA from the same sample because their ratio is interpreted. Read more about PSA itself and age thresholds in PSA, and symptoms in Early signs of prostate cancer.