Prostate-specific antigen (PSA) !

PSA is a prostate enzyme; it rises in cancer but also with benign growth, infection and handling of the gland.

Updated 2026-11-01

Key facts

A serine protease (kallikrein 3) that liquefies semen; it is specific to the prostate, not to cancer.
It rises in prostate cancer, benign prostatic hyperplasia, prostatitis, urinary retention, and after biopsy, catheterisation or recent ejaculation.
5-α-reductase inhibitors (finasteride, dutasteride) lower it by about half.
A low percentage of free PSA suggests cancer more; the rate of rise and density (PSA/volume) help interpretation.
There is no single safe cut-off: the reference value varies by laboratory and age, and screening is a shared decision.

What it measures: total serum PSA (bound to α1-antichymotrypsin plus free); sometimes free PSA separately.
Where it comes from: prostatic acinar epithelium secretes it into semen; it reaches the blood when the gland's architecture is disrupted.
Why it rises: cancer, benign enlargement (more gland volume), inflammation or infection, trauma (biopsy, cystoscopy, catheter), acute urinary retention.
Pitfalls: after prostatitis it may take weeks to fall; obesity dilutes PSA; a gentle rectal examination barely changes it.
After radical prostatectomy PSA should become undetectable; its return (biochemical recurrence) comes before clinical relapse.

PSA screening lowers mortality only slightly and carries overdiagnosis; guidelines present it as an informed choice for men in defined age groups.
Multiparametric MRI is increasingly used before biopsy when PSA is high.
Men of African ancestry and those with a family history have a higher risk of prostate cancer.

Think of the answer, then tap the question to see it.

Is PSA specific to prostate cancer?

No: it is specific to the prostate, and it also rises with benign hyperplasia, prostatitis, urinary retention or handling.

Which drugs lower PSA by about half?

5-α-reductase inhibitors such as finasteride and dutasteride.

What does a low percentage of free PSA suggest?

A higher chance of cancer, because tumour-made PSA circulates more bound to proteins.

What is expected of PSA after radical prostatectomy?

That it becomes undetectable; if it reappears, it signals biochemical recurrence.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Prostate-Specific Antigen (PSA) Test: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Prostate-specific antigen (PSA) blood test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.