PSA — prostate-specific antigen — is the best-known blood marker for the prostate, and it is often the first test men think of when prostate health comes up. But a single PSA number can be difficult to interpret on its own. Measuring both total PSA and free PSA, and looking at the ratio between them, gives a more nuanced picture and can help avoid unnecessary worry. Here is how the two work together.
What PSA is
PSA is a protein made by the prostate gland and released into the blood. Both healthy and abnormal prostate tissue produce it, which is why the test is useful but not definitive. A raised level flags that the prostate deserves attention — it does not, by itself, diagnose cancer. Many men with a raised PSA turn out to have a completely benign explanation.
Total PSA vs free PSA
PSA travels in the blood in two forms: bound to other proteins, or floating freely.
- Total PSA — all the PSA in your blood, both bound and free. This is the standard first-line measurement.
- Free PSA — the fraction circulating unbound.
- The free/total ratio — the proportion of PSA that is free. A lower ratio is generally associated with higher risk, while a higher ratio is more reassuring.
Measuring both is especially helpful when total PSA sits in a borderline range, where the ratio can help distinguish men who need further investigation from those who probably do not.
What can raise PSA besides cancer
Plenty of everyday things can push PSA up temporarily, which is why context matters so much. Common non-cancer causes include:
- An enlarged prostate (a normal part of ageing for many men),
- Prostate infection or inflammation (prostatitis),
- Recent ejaculation or vigorous exercise such as cycling,
- Recent catheter use or a urinary infection.
Because of these, doctors often recommend avoiding ejaculation and hard cycling for a couple of days before the test, and may repeat a raised result before acting on it.
Total and free PSA give a more accurate prostate risk assessment.
This test measures both total and free PSA and reports the ratio between them — a more informative approach than total PSA alone, particularly for borderline results.
Check total and free PSAThe limits of PSA
PSA testing is not perfect. It can be raised without cancer being present, and occasionally normal when a problem exists. This is why it is offered as an informed choice rather than a blanket screening programme in the UK, and why results are always considered alongside examination, imaging and, where needed, specialist assessment. Understanding these limits helps you weigh up testing sensibly.
Who should consider testing
PSA testing is worth discussing for men over 50, and earlier — from around 45 — for those at higher risk, including men with a family history of prostate cancer and men of Black ethnicity, who have a higher lifetime risk. If you have urinary symptoms such as a weak stream, frequency or getting up at night, see a doctor regardless of age. Testing is a personal decision best made with a clinician who can explain what a result would and would not tell you.
Check total and free PSA
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Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic