PSA Test — Purpose, Procedure & Normal Values | MyMedicPlus

The PSA (prostate-specific antigen) test is a blood test that measures the concentration of PSA — a serine protease glycoprotein produced exclusively by the epithelial cells of the prostate gland — in the blood. PSA is normally present in small quantities in the circulation; elevated levels may indicate benign prostatic hyperplasia (BPH), prostatitis (acute or chronic inflammation of the prostate), or prostate cancer. PSA is not cancer-specific — it is a marker of prostate gland disease and cellular disruption in general, making interpretation nuanced and context-dependent. In serum, PSA exists in two main forms: free PSA (not bound to proteins) and complex PSA (bound primarily to alpha-1-antichymotrypsin). The ratio of free to total PSA provides additional clinical information. PSA remains the most widely used tool for prostate cancer early detection and is indispensable for monitoring treatment response after radical prostatectomy, radiotherapy, or androgen deprivation therapy. However, its role in population-based screening remains debated due to its limited specificity, the risk of overdiagnosis of indolent cancers, and associated harms from unnecessary biopsies.

PSA testing is ordered for several distinct clinical purposes. For prostate cancer early detection: offered to men typically from age 50 after shared decision-making with their doctor; from age 40–45 for high-risk groups including men of African or Caribbean descent (who have a 2–3 times higher risk) and those with a first-degree relative (father or brother) diagnosed with prostate cancer before age 65; and from age 40 in men with a confirmed BRCA2 gene mutation. For lower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia or prostatitis: urinary frequency, urgency, nocturia, a weak or interrupted stream, incomplete bladder emptying, and straining. For monitoring prostate cancer after radical prostatectomy — where PSA should fall to undetectable levels (<0.1 ng/mL) within 4–6 weeks; any subsequent rise is termed biochemical recurrence and requires further evaluation. For monitoring PSA response to radiotherapy or hormone (androgen deprivation) therapy. PSA is not indicated for men with a life expectancy of less than 10 years, as the benefits of detection and treatment are unlikely to be realised.

Several activities and conditions are known to transiently elevate PSA and must be avoided before testing to prevent a misleadingly raised result. Avoid ejaculation for at least 48 hours, and ideally 72 hours, before the blood draw, as sexual activity causes a transient physiological PSA rise. A digital rectal examination (DRE) performed in the same clinical encounter should ideally be done after the blood is drawn, or the PSA measured 24 hours after DRE. Prostate biopsy causes a major, prolonged PSA elevation that can persist for 4–6 weeks — defer PSA testing for at least 4 weeks after any biopsy. Urinary tract infections, prostatitis, and cystoscopy can significantly elevate PSA — treat any active infection and wait 4–6 weeks before re-testing. Vigorous cycling or horseback riding may elevate PSA due to perineal pressure — avoid for 48 hours beforehand. Inform your doctor if you take 5-alpha reductase inhibitors (finasteride or dutasteride for BPH or hair loss), as these drugs suppress PSA by approximately 50% after 6–12 months; your doctor will apply a doubling correction factor to interpret the result accurately.

A phlebotomist or nurse draws a 3–5 mL blood sample from a vein in the antecubital fossa (elbow crease) of the arm. A tourniquet is applied briefly, the skin is cleaned with an alcohol swab, and a fine needle is inserted into the vein. The blood is collected into a serum separator (gold or red-top) tube. The procedure takes less than 5 minutes and causes minimal discomfort — a brief sharp sensation during needle insertion. The blood sample is centrifuged to separate serum and then analysed on an automated immunoassay platform using chemiluminescent or electrochemiluminescent immunoassay (CLIA or ECLIA) to measure total PSA concentration. Some laboratories additionally measure free PSA from the same sample and calculate the free-to-total PSA ratio. PSA velocity — the rate of change in PSA over serial measurements, expressed as ng/mL per year — is calculated when multiple prior results are available. Results are typically available within 24 hours.

PSA reference ranges vary by laboratory assay and patient age. Age-adjusted normal thresholds (widely used): Age 40–49: below 2.5 ng/mL; Age 50–59: below 3.5 ng/mL; Age 60–69: below 4.5 ng/mL; Age 70 and over: below 6.5 ng/mL. Traditional absolute threshold: PSA below 4.0 ng/mL — generally considered normal in men of any age; PSA 4.0–10.0 ng/mL — the 'grey zone', associated with BPH or prostate cancer; PSA above 10.0 ng/mL — high probability of prostate cancer (approximately 50–60% risk of cancer on biopsy). Free-to-total PSA ratio: below 10% — higher likelihood of prostate cancer; above 25% — more likely BPH. PSA velocity: greater than 0.75 ng/mL per year increases suspicion for prostate cancer, even within the normal PSA range. PSA density (PSA divided by prostate volume on imaging) — above 0.15 ng/mL/cc suggests cancer more likely than BPH. After radical prostatectomy, PSA below 0.1 ng/mL is considered undetectable; biochemical recurrence is defined as two successive PSA values of 0.2 ng/mL or above.

The blood draw itself carries negligible risk — minor bruising, haematoma, or vasovagal reaction are the only realistic complications. The PSA test's primary clinical limitation is its low specificity for prostate cancer. In men with PSA in the 4–10 ng/mL range, only approximately 25–30% who undergo biopsy actually have prostate cancer — meaning 70–75% have a false positive result, leading to unnecessary biopsy with associated risks (bleeding, infection, sepsis, pain, hospitalisation in up to 1–3% of cases) and significant patient anxiety. Conversely, approximately 15–25% of men with prostate cancer have a PSA below 4.0 ng/mL — a false negative rate that is particularly relevant for high-grade (Gleason 8–10) cancers that may produce disproportionately low PSA. Overdiagnosis — the detection and treatment of indolent, low-grade (Gleason 6) prostate cancers that would never have progressed to cause symptoms or death during the man's lifetime — is the most significant harm of population PSA screening programmes. Active surveillance protocols, where low-risk cancers are monitored with serial PSA, MRI, and repeat biopsy rather than treated, are now standard of care for this group.