The PSA Test: What It Measures, Normal Ranges, and What a Raised Result Means

What PSA is

Prostate-specific antigen is an enzyme produced by the cells lining the prostate gland; its normal job is to liquefy semen. A small amount leaks into the bloodstream, and the PSA test measures it in nanograms per millilitre (ng/mL).

Anything that increases the number of prostate cells, or disrupts the barrier between the gland and the blood, raises PSA. Cancer does both, which is why PSA became a cancer screening test. So does benign enlargement, and so does inflammation. PSA is therefore best understood as a measure of how much prostate tissue there is and how disturbed it is, not as a cancer detector.

Reference ranges

There is no true normal value. The traditional cut-off of 4.0 ng/mL came from early studies and is still used, but it misses a proportion of cancers below it and flags many benign glands above it. Age-adjusted ranges are widely used instead, because PSA rises with age as the gland enlarges:

Guidelines in different countries use somewhat different thresholds — the UK, for example, uses 3.0 ng/mL for men aged 50–69 as the level prompting referral. A baseline PSA in a man's forties also predicts long-term risk: a level below 1 ng/mL at 45 is associated with a very low chance of aggressive cancer over the following decades.

Why PSA rises

Non-cancer causes account for most raised results:

• Benign prostatic hyperplasia — the larger the gland, the higher the PSA. See enlarged prostate.
• Prostatitis and urinary tract infection — can raise PSA markedly and for weeks. See prostatitis.
• Ejaculation within the previous 48 hours.
• Vigorous cycling or other perineal pressure.
• Rectal examination, catheterisation, cystoscopy or prostate biopsy shortly before the test.
• Urinary retention.
• Age, through gland growth.

And two things lower it:

• 5-alpha reductase inhibitors (finasteride, dutasteride) roughly halve PSA after six months; the measured value should be doubled for interpretation.
• Obesity modestly lowers PSA through dilution in a larger blood volume.

How a result is interpreted

A single raised PSA is rarely acted on alone. Doctors consider:

• Repeat testing after six to eight weeks, avoiding the triggers above, to exclude a transient rise.
• PSA velocity — how fast it is rising. A rise of more than about 0.75 ng/mL per year, or a doubling within a couple of years, is more concerning than a stable elevation.
• PSA density — PSA divided by prostate volume from ultrasound or MRI. A high PSA from a large benign gland gives a low density; a high PSA from a small gland is more suspicious.
• Free PSA percentage — PSA circulates bound to proteins or free; cancer produces relatively more bound PSA. A free fraction below about 10–15% raises suspicion; above 25% lowers it. Useful in the 4–10 ng/mL range.
• Prostate examination for nodules or asymmetry.
• Multiparametric MRI — now standard in many countries before biopsy. A normal MRI in a man with a moderately raised PSA can safely avoid biopsy; an abnormal one guides a targeted biopsy.
• Newer blood and urine markers (PHI, 4Kscore, PCA3) in some settings.

Biopsy is the only way to confirm cancer. Modern practice tries to biopsy fewer men, and to biopsy the right ones.

The screening question

PSA screening reduces deaths from prostate cancer modestly — the large European trial found roughly one death prevented per 570 men screened over 16 years — but at a cost. Many cancers it finds are slow-growing and would never have caused symptoms; treating them exposes men to incontinence and erectile dysfunction for no benefit. Biopsies carry infection risk. And false-positive results cause anxiety and further tests.

For these reasons, most guidelines recommend shared decision-making rather than routine screening: men aged roughly 50–70 (earlier for Black men and those with a family history) should be offered information and decide with their doctor. Men over 70 or with less than 10–15 years' life expectancy generally do not benefit. Where screening is chosen, testing every two to four years is usually sufficient, and active surveillance rather than immediate treatment is now standard for low-risk cancers found.

What to do with your result

A PSA within the age-appropriate range needs nothing more than a repeat at the agreed interval. A raised result means a repeat test with the triggers avoided, then a conversation about MRI if it stays up. A rapidly rising PSA, a hard or irregular gland on examination, or a PSA above 10 warrants prompt referral. Symptoms of enlargement — weak stream, night-time urination — are assessed on their own merits, since PSA does not measure them.

Frequently asked questions

References