Free PSA

What is free PSA?

PSA (prostate-specific antigen) is a protein produced by the prostate gland that circulates in the blood in different forms. Most of the PSA in the blood is bound to other proteins, while a small portion circulates in free form. The free PSA test measures the amount of this unbound portion.

Free PSA is not interpreted on its own; it is expressed as a ratio to total PSA measured in the same blood sample, and the result is given as a percentage. Studies have shown that the free PSA ratio tends to be lower in prostate cancer than in benign prostate enlargement. The measurement is performed on serum using immunoassay methods compatible with total PSA. The free PSA value is also used in some risk calculations, such as the Prostate Health Index.

When is a free PSA test ordered?

Free PSA is mostly ordered in men whose total PSA is slightly elevated or borderline, to help decide whether further investigations such as a prostate biopsy are needed. This ratio gives the doctor an additional clue as to whether a high PSA may be due to benign prostate enlargement or to another cause. It is not a screening or diagnostic test on its own.

• Total PSA that is slightly elevated or borderline
• PSA values that are gradually rising compared with previous measurements
• Monitoring of men whose earlier biopsy was clear but whose PSA remains elevated
• Additional assessment in people with urinary complaints due to prostate enlargement

How do you prepare for a free PSA test?

No fasting is required for free PSA, but certain activities that affect the prostate are important. Because ejaculation and activities that put pressure on the prostate, such as cycling or horse riding, can temporarily change PSA values, it is recommended to avoid them for 48 hours before the test. Ask your doctor when the test should be done after procedures such as a digital rectal examination, urinary catheter insertion, cystoscopy or prostate biopsy; if you have a urinary tract infection or prostatitis, the measurement is usually postponed until after recovery.

Before the sample is taken, mention the medicines you use (especially those used to treat prostate enlargement) and any supplements containing biotin (B7). Because free PSA can change if the blood sample is left standing for a long time, it is important that the sample is processed promptly. You can also choose to have our nurse come to your home or workplace for this blood sample.

What does a free PSA result mean?

There is no reference range used for free PSA on its own; for this reason, no separate range is shown on this page, and the result is evaluated together with total PSA as the free/total ratio. A higher ratio suggests that the elevated PSA is more likely to be due to causes such as benign prostate enlargement. A lower ratio, on the other hand, may indicate an increased likelihood of prostate cancer and may lead the doctor to plan further investigations.

The ratio helps in estimating probability; on its own, it does not show whether or not cancer is present. The thresholds used to interpret the ratio may vary with age, prostate volume and the method used by the laboratory. When making a decision, your doctor considers total PSA, examination findings, a prostate MRI if needed, and your family history together. The meaning of your free PSA ratio must be interpreted by a doctor together with your symptoms and other investigations.