The PSA Test Explained: What It Measures and Questions to Ask Your Doctor

Few tests cause as much confusion as the PSA. Some men have it every year without knowing it was ordered. Others have been told it's unreliable and never had it. The truth sits in the middle: it's a useful test with real limits, and the right choice depends on you.

What PSA actually is

PSA stands for prostate-specific antigen, a protein made by cells in the prostate gland. Small amounts normally leak into the blood. The test is an ordinary blood draw that measures how much is there, in nanograms per millilitre (ng/mL).

The key thing to understand: PSA is specific to the prostate, not to cancer. Anything that makes the prostate bigger, busier or irritated can push the number up.

Why PSA can be high without cancer

According to the National Cancer Institute, PSA levels can rise because of:

• Benign enlargement, which is very common with age (see What the Prostate Does)
• Inflammation or infection of the prostate (prostatitis)
• Age itself, since PSA tends to drift up over the years
• Recent pressure on the area, such as a long bike ride or some medical procedures, so ask whether you should avoid anything before the test
• Prostate cancer

Some medicines can also lower PSA, which matters when reading results. Tell your doctor everything you take.

Is there a "normal" number?

Not a single one. For years, 4.0 ng/mL was used as a rough cut-off, but men can have prostate cancer below it and no cancer well above it. Doctors now look at the whole picture: your age, how the number changes over time, the size of your prostate, your family history and other tests. A single reading is a starting point for a conversation, not a verdict.

What the guidelines say

The U.S. Preventive Services Task Force (USPSTF), an independent panel that reviews screening evidence, published its current prostate recommendation in 2018:

Other organisations, including the American Cancer Society, suggest starting that conversation earlier, around 45, for men at higher risk: Black men and men whose father or brother was diagnosed with prostate cancer at a younger age. Guidelines are periodically reviewed, so ask your doctor what currently applies to you.

The trade-off, in plain terms

The possible benefit: finding an aggressive cancer early, when there are more options.

The possible downsides: false alarms that lead to worry and more testing, including biopsies, which carry their own risks; and finding slow-growing cancers that might never have caused a problem in your lifetime, sometimes leading to treatment you didn't need. Today, many low-risk cancers are watched closely rather than treated right away, which has reduced that second risk.

Questions to ask your doctor

1. Given my age, family history and health, what's my personal risk?
2. What would you recommend for me, and why?
3. If my PSA comes back high, what would happen next?
4. Should I avoid anything (exercise, cycling) before the blood draw?
5. Do any of my medicines affect the result?
6. If I've had PSA tests before, how has my number changed?
7. How often would we repeat it?