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# 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.

## In detail

- 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.

**Also called**
PSA, Free and total PSA

## Clinical notes

- 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.

## Related conditions

- [Prostate cancer](https://durgical.com/en/conditions/prostate-cancer/)
- [Benign prostatic hyperplasia](https://durgical.com/en/conditions/benign-prostatic-hyperplasia/)
- [Prostatitis](https://durgical.com/en/conditions/prostatitis/)
- [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/)

## Related

- [Tumour markers: principles of use](https://durgical.com/en/biochemistry/topics/tumour-markers-principles-of-use/)
- [Alkaline phosphatase (ALP) as a lab test](https://durgical.com/en/biochemistry/topics/alkaline-phosphatase-as-a-lab-test/)

## Test yourself

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.

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

Sources: [Prostate-Specific Antigen (PSA) Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/prostate-specific-antigen-psa-test/) (MedlinePlus, US National Library of Medicine, 2026); [Prostate-specific antigen (PSA) blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003346.htm) (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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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/prostate-specific-antigen/