Summary
Prostate-Specific Antigen (PSA) is a protein produced by the prostate gland. Total PSA in the blood is the principal marker used to assess prostate health. A raised PSA can indicate prostate cancer, but more often reflects benign enlargement (BPH) or inflammation (prostatitis). PSA is used for early detection, to guide further investigation, and to monitor men after prostate cancer treatment.
PSA is normally secreted into semen, with only small amounts entering the blood. Conditions that disrupt prostate architecture — cancer, benign enlargement, infection, or even recent ejaculation, cycling, or a rectal examination — raise blood PSA.
Because PSA is prostate-specific but not cancer-specific, interpretation requires context: age, prostate size, the rate of change over time (PSA velocity), and the proportion of free PSA. The free:total PSA ratio helps distinguish cancer (lower free PSA) from benign enlargement (higher free PSA).
PSA-based testing involves trade-offs: it can detect significant cancers early, but also detects slow-growing cancers that may never cause harm, and can lead to further tests and anxiety. Decisions about PSA testing are best made with an understanding of these benefits and limitations.
What It Is
PSA is a serine protease (kallikrein-3) produced almost exclusively by prostate epithelial cells, where it liquefies semen. Disruption of the normal prostate glandular architecture allows PSA to leak into the circulation in greater amounts.
In blood, PSA exists as free PSA and PSA complexed to proteins. Prostate cancer tends to produce more complexed PSA, lowering the free:total ratio; benign enlargement tends to produce more free PSA. Age-specific reference ranges, PSA density (PSA relative to prostate volume), and PSA velocity (rate of rise) all refine interpretation.
Commonly used age-related upper limits: 0–2.5 ng/mL (40s), up to ~3.5 ng/mL (50s), ~4.5 ng/mL (60s), ~6.5 ng/mL (70s). A total PSA above the age-specific threshold, a rapidly rising PSA, or a low free:total ratio prompts further assessment such as MRI and biopsy.
Functions
Prostate cancer detection
PSA is the principal blood marker used to raise or lower suspicion of prostate cancer and guide further investigation.
Treatment monitoring
After prostate cancer treatment, PSA is used to detect residual or recurrent disease — a rising PSA signals recurrence.
Benign prostate assessment
Helps evaluate benign prostatic enlargement and prostatitis, which are common causes of a raised PSA.
Risk refinement
PSA velocity, density, and the free:total ratio refine cancer risk and reduce unnecessary biopsies.
Reference Ranges
Total PSA
Measured in ng/mL| Status | Range (ng/mL) | Range (μg/L) | What it means |
|---|---|---|---|
| Low | < 2.5 | < 2.5 | Low PSA — prostate cancer less likely (though not excluded). |
| Borderline | 2.5–4.0 | 2.5–4.0 | Borderline — interpret with age, free:total ratio, and trend; may warrant further assessment. |
| Elevated | 4.0–10 | 4.0–10 | Elevated — investigate further (MRI, specialist review); cancer and benign causes both possible. |
| High | > 10 | > 10 | Significantly raised — higher likelihood of prostate cancer; prompt urological assessment. |
Reference thresholds are age-dependent and PSA is prostate-specific but not cancer-specific. Avoid ejaculation, cycling, and DRE before testing. A borderline result should be repeated. Interpret with free:total ratio, velocity, and clinical assessment.
Symptoms of Imbalance
PSA is often raised before symptoms appear; urinary symptoms more commonly reflect benign enlargement than cancer.
- A low PSA usually reflects normal prostate health
- Does not entirely exclude cancer
- Often no symptoms (especially early cancer)
- Urinary frequency and urgency
- Difficulty starting or weak urine flow
- Getting up at night to urinate (nocturia)
- Blood in urine or semen
- Pelvic or perineal discomfort (prostatitis)
- Bone pain (advanced prostate cancer)
Causes of Imbalance
- Normal prostate
- 5-alpha-reductase inhibitor medication (finasteride, dutasteride — roughly halve PSA)
- Benign prostatic hyperplasia (BPH) — the most common cause
- Prostatitis (prostate inflammation or infection)
- Prostate cancer
- Recent ejaculation, vigorous cycling, or rectal examination
- Urinary tract infection or retention
- Increasing age (larger prostate)
FAQs
Not necessarily. PSA is specific to the prostate but not to cancer. The most common cause of a raised PSA is benign prostatic enlargement, which is very common with age. Prostatitis (inflammation or infection), recent ejaculation, cycling, or a rectal examination can also raise it. A high PSA indicates the need for further assessment — often an MRI and specialist review — rather than a diagnosis of cancer in itself.
Several everyday factors can temporarily raise PSA. It is best to avoid ejaculation for 48 hours, vigorous cycling for 48 hours, and to have the test before (not after) a digital rectal examination. Active urinary infection also raises PSA, so testing is usually deferred until any infection has cleared. A borderline result is often repeated under these controlled conditions before any decisions are made.
PSA circulates in free and protein-bound forms. Prostate cancer tends to produce relatively more bound PSA, lowering the proportion that is free. So a low free:total ratio raises the suspicion of cancer, while a higher ratio is more reassuring and suggests benign enlargement. This ratio is particularly helpful when the total PSA is in the borderline range, helping decide whether further investigation is needed.
PSA testing involves a balance of benefits and harms. It can detect significant cancers early, but it can also detect slow-growing cancers that may never cause harm, leading to further tests, biopsies, and anxiety. There is no formal national screening programme in the UK, but men can request testing after an informed discussion of these trade-offs. Men with a family history or other risk factors may particularly wish to consider it.
References
- Mottet N, et al. EAU-EANM-ESTRO-ESUR-SIOG guidelines on prostate cancer. Eur Urol. 2021;79(2):243–262. View source
- Catalona WJ, et al. Use of the percentage of free prostate-specific antigen to enhance differentiation of prostate cancer from benign prostatic disease. JAMA. 1998;279(19):1542–1547. View source
- Ilic D, et al. Prostate cancer screening with prostate-specific antigen (PSA) test: a systematic review and meta-analysis. BMJ. 2018;362:k3519. View source