PSA (Prostate-Specific Antigen)

PSA is a protein produced by both healthy and cancerous prostate cells, measured in nanograms per millilitre (ng/mL). It is a screening signal — not a cancer diagnosis — used to decide whether further investigation (free PSA ratio, multiparametric MRI, biopsy) is warranted. Australian guidelines (RACGP, Cancer Council Australia) use age-adjusted thresholds rather than a single cut-off because PSA naturally rises with age as the prostate enlarges.

PSA is the central marker for prostate cancer screening in Australian men aged 50–69 (or 45+ with first-degree family history), recommended only after a shared-decision conversation with the GP. It is also monitored after a confirmed prostate cancer diagnosis to track treatment response, and in men on testosterone replacement therapy where prostate effects must be tracked. PSA velocity (year-on-year change) is often more informative than the absolute value — a velocity > 0.75 ng/mL/year is more concerning than a single elevated reading.

Many causes of an elevated PSA are benign and reversible. Common temporary causes: ejaculation within 48 hours of the test (raises PSA by 0.5–1.0 ng/mL), recent vigorous cycling or horse riding, urinary tract infection, recent digital rectal examination, urinary catheterisation, and acute prostatitis (which can briefly raise PSA into the double digits). Persistent causes: benign prostatic hyperplasia (BPH — the most common cause of mildly raised PSA in men over 50), chronic prostatitis, prostate cancer (raised PSA does not equal cancer — only ~25% of men with PSA in the 4–10 ng/mL range turn out to have cancer on biopsy), and rarely urinary retention or recent prostate procedure. The standard pathway after an unexpectedly raised PSA: repeat in 1–3 months with the test-day precautions, then check free PSA if total is 4–10, then multiparametric MRI before any biopsy is considered.

Low PSA is generally reassuring and does not require investigation. PSA is suppressed by 5-alpha reductase inhibitors used for benign prostatic hyperplasia and male-pattern hair loss — finasteride and dutasteride lower PSA by 30–50%. Men taking these medications should double their PSA result to estimate the equivalent untreated value when interpreting age-adjusted thresholds. Very low PSA in younger men with severe lower urinary tract symptoms occasionally points to prostate atrophy.

For asymptomatic men aged 50–69 (or 45+ with family history), Australian guidelines recommend offering PSA screening every 1–2 years after a shared-decision conversation. Medicare covers one screening test per year under MBS item 66655. Men with a previous elevated result, family history, or symptoms can be retested at any frequency. Men on TRT should have PSA measured at baseline, at 3 and 6 months after starting, then every 6–12 months (Endocrine Society of Australia). Men diagnosed with prostate cancer follow individualised monitoring schedules from their urologist (commonly every 3 months in the first year). Always observe a 7-day window of no ejaculation, no cycling, no UTI symptoms and no recent rectal exam before the test for the most accurate result.

Always interpret PSA alongside age-adjusted thresholds and free-PSA ratio (when total PSA is 4–10 ng/mL). On TRT panels, PSA is measured alongside testosterone, oestradiol, haematocrit, and LH/FSH (at baseline). After prostate cancer diagnosis or treatment, PSA velocity and PSA doubling time become the key monitoring metrics rather than the absolute value.