Prostate-Specific Antigen (PSA)
Also known as: Total PSA, Free PSA, PSA velocity
PSA is a protein produced by prostate cells and measured in blood as part of prostate cancer screening and monitoring. Interpreting PSA requires considering age, prostate size, rate of change, and other factors — a single number rarely tells the full story.
Venous blood (serum separator tube)
24–48 hours
Not required
Hormones
Reference Ranges
| Measurement | Reference Range | Unit |
|---|---|---|
| Age 40–49 | ≤ 2.5 | ng/mL |
| Age 50–59 | ≤ 3.5 | ng/mL |
| Age 60–69 | ≤ 4.5 | ng/mL |
| Age 70–79 | ≤ 6.5 | ng/mL |
Reference ranges are typical adult values. Your laboratory may use slightly different intervals — always use your lab's reported reference.
What This Test Measures
PSA is a serine protease produced by both normal and malignant prostate cells to liquefy semen. Most PSA stays in the prostate, but some leaks into the bloodstream. Cancer disrupts normal glandular architecture, allowing more PSA to reach the bloodstream. Benign prostatic hyperplasia (BPH), prostatitis, and biopsy all also raise PSA — making it a sensitive but non-specific marker.
When Is This Test Ordered?
- Prostate cancer screening in men 50–74 (shared decision-making with physician)
- Monitoring response to prostate cancer treatment (surgery, radiation, hormone therapy)
- Detecting cancer recurrence after treatment
- Evaluating lower urinary tract symptoms alongside prostate size
When Results Are High
PSA above age-adjusted reference raises suspicion for prostate cancer, but also occurs in BPH (50%), prostatitis, and recent catheterisation. PSA density (PSA ÷ prostate volume on ultrasound) and free:total PSA ratio improve specificity. A free:total ratio below 10% substantially raises cancer risk.
When Results Are Low
Low PSA is generally reassuring. 5-alpha reductase inhibitors (finasteride, dutasteride) halve PSA values — always disclose these medications to your doctor for accurate interpretation.
The debate around PSA screening
Randomised trials (PLCO, ERSPC) produced conflicting results on PSA screening benefit vs. harm from overdiagnosis. Current guidance from USPSTF (2018) recommends shared decision-making for men aged 55–69; the AUA supports informed screening from age 50 (earlier for high-risk men). The decision involves weighing cancer detection benefit against biopsy risks and overdiagnosis of indolent cancers that would never have caused harm.
Factors That Can Affect Your Result
- Digital rectal exam (DRE) raises PSA — blood should be drawn before examination
- Ejaculation within 48 hours raises PSA by 0.4–1.0 ng/mL
- Prostatitis can raise PSA 10-fold
- Finasteride/dutasteride reduce PSA by 50% — double the measured value to estimate true baseline
- Needle biopsy raises PSA to very high levels for 4–6 weeks
Tracking This Test Over Time
PSA velocity — the rate of rise over time — is as important as the absolute level. A rise of more than 0.75 ng/mL per year increases suspicion for cancer regardless of absolute level. Track your PSA trend in Looms and share the trend — not just the latest number — with your urologist.
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Medical disclaimer
This page is for educational purposes only and does not constitute medical advice. Reference ranges vary between laboratories, and results must be interpreted in the context of your symptoms, history, and other tests. Always discuss your results with your healthcare provider. Content reviewed by the Looms medical team, 2026-06-01.