Prostate-specific antigen (PSA) is a protein produced by prostate cells — both normal and cancerous. A PSA blood test measures the level of this protein in your blood and is the most widely used test for prostate cancer screening. It's also one of the most debated tests in medicine.
Understanding what the test can and can't tell you is essential for making an informed decision about whether to have it and what to do with the result.
What counts as a normal PSA level?
PSA levels are reported in nanograms per millilitre (ng/mL). There is no single 'safe' threshold — risk is a spectrum — but most guidelines use age-adjusted reference ranges:
- **Under 50:** below 2.5 ng/mL is generally considered normal
- **50–59:** below 3.5 ng/mL
- **60–69:** below 4.5 ng/mL
- **70 and above:** below 6.5 ng/mL
- A level above 10 ng/mL is associated with a significantly higher probability of prostate cancer — but even then, the majority of biopsies in this range are benign.
PSA is not prostate-cancer-specific
The name is misleading: PSA is prostate-specific, not cancer-specific. A raised PSA can be caused by several non-cancerous conditions:
- Benign prostatic hyperplasia (BPH) — an enlarged prostate
- Prostatitis — inflammation or infection of the prostate
- Recent ejaculation (within 48 hours)
- Vigorous cycling or horseback riding
- A urinary tract infection
- A recent urinary catheter or cystoscopy
PSA velocity and doubling time
A single PSA reading is a snapshot. More informative is how quickly it's rising — PSA velocity (the rate of rise per year) and PSA doubling time. A PSA that rises rapidly (doubling within one to two years) is more clinically concerning than one that is stable at the same level over many years. This is why tracking serial PSA values over time is as important as the number itself.
Free vs total PSA
PSA exists in the blood in two forms: free (unbound) and total (free plus bound to proteins). Prostate cancer tends to produce proportionally less free PSA. If total PSA is borderline, the free-to-total PSA ratio helps refine the risk estimate. A ratio below 10% suggests higher cancer probability; above 25% is more reassuring.
Should you have a PSA test?
Major clinical bodies — including the UK's NHS and the US Preventive Services Task Force — take different positions on routine PSA screening, reflecting a genuine trade-off between earlier cancer detection and the risk of overdiagnosis and overtreatment of slow-growing cancers that would never have caused harm.
The consensus is that men aged 50–70, and men at higher risk (Black ethnicity, first-degree relative with prostate cancer) from age 45, should have an informed conversation with their doctor about whether to test — understanding both the potential benefits and the likelihood of a false alarm. A raised PSA typically leads to an MRI scan before any biopsy is considered.