The PSA test is one of the most widely used tools in prostate health, and also one of the most misunderstood. A raised result does not mean a man has cancer, and a normal result does not rule it out. Understanding what the test can and cannot tell you helps you make sense of your own numbers.
What PSA is
PSA stands for prostate specific antigen. It is a protein made by cells in the prostate, and its main role is to keep semen fluid. Most PSA stays in the semen, but a small amount leaks into the bloodstream. The PSA test measures how much is in the blood, in nanograms per millilitre (ng/ml).
Both normal and cancerous prostate cells make PSA. That is the key reason the test cannot diagnose cancer by itself.
Why PSA levels rise
Several things can raise PSA, including:
- Age: the prostate tends to grow over time, so PSA often rises gently with age.
- Benign prostatic enlargement: a larger gland makes more PSA.
- Prostatitis or urine infection: inflammation can push PSA up sharply for a while.
- Recent activity: ejaculation, vigorous cycling or a prostate examination shortly before the test.
- Prostate cancer: cancer cells can release more PSA into the blood.
Because of this, doctors usually ask men to avoid ejaculation and strenuous exercise for 48 hours before a test, and to delay testing if they have a urine infection.
What counts as a normal result
There is no single cut-off that suits every man. In the UK, doctors use age-related thresholds as a guide, with higher levels considered acceptable as men get older. The NHS page on the PSA test explains the general approach.
Doctors may also look at:
- PSA density: the PSA level compared with the size of the prostate, usually measured on MRI. A high PSA in a large gland may be less concerning than the same PSA in a small one.
- PSA velocity: how quickly the level is changing over time.
- Free to total PSA ratio: a further blood test that can add information in some cases.
Why one reading is rarely enough
PSA can vary from one test to the next. A single raised result is often repeated after a few weeks to see whether it settles. A trend over time usually tells a doctor more than any one number.
PSA is also only one part of the picture. Age, family history, ethnicity, examination findings and general health all shape what a result means for an individual man.
What happens after a raised PSA
If your PSA is higher than expected, your GP may refer you to a urologist. The next step is usually an MRI scan of the prostate. MRI helps to show whether there is an area that looks suspicious and whether a biopsy is needed. Some men with a normal MRI can safely avoid a biopsy and continue with PSA monitoring.
Our articles on combining MRI and PSMA PET scans and significant cancer after a negative MRI look at how imaging is used in more detail.
Can the PSA test cause worry?
It can. A raised result that turns out to be harmless can still cause anxiety, and a borderline result can leave men unsure what to do. Prostate Cancer UK has clear information on the pros and cons of testing. Talking through your result with a specialist, and understanding your own risk, usually helps.
PSA after treatment
PSA is also very useful after treatment for prostate cancer. After surgery, PSA should fall to a very low level, and regular tests are used to check that it stays there. Our prostate cancer page explains how follow-up works.
Getting your result explained
If you have had a PSA test and would like a specialist view on what it means, Professor Prokar Dasgupta can review your results and history at The London Clinic. Our guide to smart screening for prostate cancer explains a modern approach to testing. Please contact the clinic to arrange a consultation.