PSA

Blood test

Also known as: Prostate-specific antigen, Total PSA, Percent free PSA

There is no single guideline cutoff for PSA; your result is read with a clinician in light of your age, earlier results, prostate size and medicines.

PSA is a protein made by the prostate, so this is a test for men. Some leaks into the blood, and the amount rises with age, prostate size and cancer. It is the first-line screening test for prostate cancer, but a raised result is not a diagnosis.

What it tells you

Total PSA counts all the PSA in the blood. Most of it is bound to other proteins, and a smaller part circulates free.
PSA is specific to the prostate, not to cancer. An enlarged prostate, inflammation and older age all raise it.
Percent free PSA is the free part as a share of the total. It tends to be lower in cancer than in a benign enlarged prostate.
Its main use is helping with the biopsy decision when total PSA sits in a middle "grey zone."
A US task force says men aged 55 to 69 should decide about screening with their clinician. It advises against routine screening from age 70.
Screening lowers the chance of dying from prostate cancer, but the benefit for each man is small. It also finds slow cancers that would never have caused harm.

What can throw it off

Medicines called 5-alpha reductase inhibitors, such as finasteride and dutasteride, lower PSA by about half. A result has to be read with that in mind.
Testosterone therapy raises it slightly, mostly in the first year.
A larger prostate and older age raise it.
A prostate biopsy can raise it falsely, so blood is not drawn soon after one.
Recent ejaculation raised total and free PSA for a few hours in one study. No guideline sets a waiting period.
Methods differ between labs, so switching labs can shift results.

Evidence

Screening for prostate cancer

Strong human evidenceCEBM Level 1a

In a European trial of over 162,000 men followed for 23 years, screening cut prostate cancer deaths by about 13%. About 456 men had to be invited to prevent one death. A review of 6 trials found a similar drop but no clear change in deaths from any cause.

Percent free PSA in the biopsy decision

Some human evidenceCEBM Level 2a

A review of 66 studies found percent free PSA did better than total PSA alone in the grey zone. But when set to catch almost all cancers, it cleared few men who did not have cancer. Most studies came from men already referred for biopsy.

How testosterone therapy changes PSA

Strong human evidenceCEBM Level 1b

In a trial of over 5,200 men with low testosterone, treatment raised PSA slightly in the first year compared with placebo. Rates of high-grade prostate cancer did not differ significantly, but there were few cases. The trial left out men with a raised PSA or past prostate cancer.

Limits

It is specific to the prostate, not to cancer. An enlarged prostate, inflammation and recent procedures raise it, and most men with a raised PSA do not have serious cancer.
A normal result does not rule out cancer.
Screening also finds low-grade cancers that would never have caused harm.
Medicine effects are large and easy to miss. A 5-alpha reductase inhibitor halves the number, and testosterone raises it a little in the first year.
The benefit for each man is small. In the largest trial, hundreds of men had to be invited to screening to prevent one death.

References

Reviewed by Shubham Gupta, MD — Founder & President · November 5, 2026

This page is for education only. It is not medical advice. Decisions about any treatment belong with a physician who knows your history.