💡 In one sentence: PSA is a protein produced by prostate gland cells — a blood test measuring it screens for prostate cancer and monitors the prostate's health, though elevated PSA has many causes beyond cancer.
What Does PSA Measure?
PSA (Prostate-Specific Antigen) is a glycoprotein enzyme produced by prostate cells — both normal and cancerous. Its physiological function is to liquefy semen after ejaculation. Small amounts leak into the bloodstream, where they can be measured. PSA is prostate-specific (produced only by prostate tissue) but not cancer-specific — it is elevated by BPH (benign enlargement), prostatitis, recent ejaculation, vigorous cycling, and prostate massage, in addition to cancer. Interpreting PSA requires clinical context: absolute level, age-specific thresholds, PSA density (PSA divided by prostate volume on ultrasound), and PSA velocity (rate of rise over time) are all considered together.
Understanding Abnormal Results
⬆️ High PSA may indicate:
Mildly elevated (4–10 ng/mL)Further evaluation needed: prostate ultrasound, DRE, PSA density calculation; biopsy if density or other features are concerning
Moderately elevated (10–20 ng/mL)High suspicion for cancer — urology referral and prostate biopsy recommended
Markedly elevated (>20 ng/mL)Very high cancer probability — staging CT and bone scan alongside biopsy to assess spread
Frequently Asked Questions
Does a PSA of 5 mean I have prostate cancer?
Not necessarily. A PSA of 5 ng/mL falls in the "grey zone" where BPH (benign enlargement) and prostatitis are common causes alongside cancer. About 25% of men with PSA 4–10 have cancer on biopsy — meaning 75% do not. The critical next step is a prostate ultrasound (to measure gland volume and calculate PSA density) and a digital rectal examination. If PSA density is low and DRE is normal, active surveillance rather than immediate biopsy may be appropriate.
Can I eat before a PSA test?
Yes — PSA is not affected by food, so no fasting is needed. However, ejaculation in the 48 hours before the test temporarily raises PSA by 0.4–1.0 ng/mL, and vigorous cycling or prolonged perineal pressure can also raise it transiently. Abstain from ejaculation and avoid cycling for 48 hours before the test for an accurate result.
If I am on finasteride for hair loss, does it affect my PSA?
Yes — significantly. Finasteride (Propecia for hair loss, Proscar for BPH) and dutasteride reduce PSA by approximately 50% after 6 months of use. If your PSA was measured on finasteride, your doctor must multiply the reported value by 2 to estimate the true PSA equivalent. Failure to account for this can lead to dangerously falsely reassuring readings that miss significant prostate cancer.
Is PSA screening recommended for all men?
Current guidelines recommend PSA screening discussions (rather than blanket screening) for: all men over 50 who ask about it and have a life expectancy above 10 years; men over 45 of African descent (higher prostate cancer risk and typically more aggressive disease); and men over 40 with a first-degree relative who had prostate cancer. The decision should be made individually with your doctor, weighing the benefits of early detection against the risk of unnecessary biopsy and overtreatment of slow-growing cancers.