PSA testing: what it can and can't tell you

PSA is the most contested test in men's health — useful enough that guidance supports offering it, imprecise enough that the same guidance insists the decision be yours. Both halves are true, and this article is about holding them together.

What PSA measures

Prostate-specific antigen is a protein made by the prostate; a small amount normally circulates in blood. Prostate cancer usually raises it — which is the test's value — but so do several things that are not cancer, which is its problem.

Why the number is noisy

PSA rises with age as the prostate naturally enlarges. It rises with benign enlargement, with prostate inflammation or urinary infection, and transiently after ejaculation, vigorous cycling, or a prostate examination. A single raised reading therefore has many innocent explanations — which is why the standard response to one is repeating the test after an interval, not alarm.

The honest trade, both directions

The benefit is real: PSA testing detects prostate cancer earlier, and trial evidence supports a modest reduction in prostate cancer deaths from organised testing.

The harms are real too: false alarms leading to biopsies that find nothing; and overdiagnosis — finding slow cancers that would never have caused harm in a man's lifetime, whose treatment carries lasting consequences. Modern pathways — repeat testing, MRI before biopsy, active surveillance of low-risk findings — have shrunk these harms considerably, but not to zero.

This is why Australian guidance lands where it does: for men aged 50 to 69 who decide to test after weighing benefits and harms, PSA every two years — with the conversation starting earlier, around 45, where family history raises the stakes. Not a default for everyone; a considered choice for each man. Testing much beyond 70, or in men with limited life expectancy, tips the balance the other way.

If a result comes back raised

One raised PSA is a repeat, not a diagnosis. A confirmed elevation is a GP conversation about the pathway — which today runs through assessment and usually imaging before any biopsy decision, and through specialist hands. At no point does a number alone settle anything.

What PSA won't tell you

• Whether you have cancer. It raises or lowers suspicion; tissue diagnosis is a different, later step.
• Whether a cancer matters. PSA cannot separate the dangerous from the indolent — the pathway after it exists to make that distinction.
• Anything, from one reading. Confirmed trend beats single value, here more than almost anywhere.
• What you should choose. The evidence supports either informed decision. What it does not support is testing by default, without the conversation — or a symptom being handled as screening. Urinary symptoms or concerns are a GP visit now, whatever any prior PSA said.

The bottom line

PSA is a legitimate, imperfect early-warning system whose use is rightly a personal decision made with a GP — from 50 for most men, from about 45 with family history, every two years for those who opt in. The test is simple. The decision deserves better than being made by default in either direction.