What the PSA test shows
PSA (prostate-specific antigen) is a protein — the enzyme kallikrein-3 — made almost entirely by prostate cells, where it keeps semen liquid. A little leaks into the blood, and the test measures that. Because only prostate tissue makes it in quantity, PSA is organ-specific: a raised level points straight at the prostate, which MedlinePlus describes as a protein normally present in blood at a low level.
The catch is that PSA is organ-specific but not cancer-specific. Anything that irritates or enlarges the prostate — not only cancer — can raise it, so a high value is a prompt to investigate, not a diagnosis. That sets PSA apart from the other markers in this panel: CEA and CA 19-9, for instance, are neither organ- nor cancer-specific, while PSA at least tells you which organ to examine. Labs report total PSA, which can be split into free and bound fractions to refine a borderline result.
PSA normal range
PSA is reported in ng/mL, numerically identical to the SI unit µg/L (1 ng/mL = 1 µg/L), so US and European reports mean the same thing. It is essentially a male test — people without a prostate have very low or undetectable levels. There is no clean line between normal and abnormal; risk rises continuously with the number. The traditional cutoff is 4.0 ng/mL, but because the prostate grows with age, many labs apply age-specific upper limits:
| Age (men) | Common upper limit, ng/mL (= µg/L) |
|---|---|
| 40–49 | ~2.5 |
| 50–59 | ~3.5 |
| 60–69 | ~4.5 |
| 70–79 | ~6.5 |
A value under about 4.0 ng/mL is widely treated as normal, per the NCI, though a lower age-adjusted limit catches more early cancers in younger men and avoids over-testing older ones, and PSA is read as a trend over time, not one snapshot. Reference ranges depend on the lab, sex and age — read your result against your own report.
Why PSA is high
A raised PSA is common and, most of the time, is not cancer. Roughly by frequency:
- Benign prostatic hyperplasia (BPH) — the age-related enlargement affecting most older men. More prostate tissue makes more PSA; this is the commonest reason for a mildly-to-moderately raised value.
- Prostatitis — inflammation or infection of the prostate, which can push PSA up sharply, then settle after treatment.
- Urinary tract infection — a bladder or urine infection can lift PSA until it clears.
- Recent activity and procedures — ejaculation (up to 48 hours before), cycling, a catheter, a digital rectal exam and especially a prostate biopsy all raise PSA briefly, so a test is best delayed after these.
- Prostate cancer — the reason the test exists. The higher the PSA and the faster it rises, the greater the chance; but only a minority of raised results prove to be cancer, as StatPearls notes.
When is it urgent? A very high PSA — in the tens or hundreds — raises strong concern for cancer that may have spread and warrants prompt urology review, as does a hard nodule on examination or a PSA rising steadily on repeat tests. One caveat: 5-alpha-reductase inhibitors (finasteride, dutasteride) roughly halve PSA, so a “normal” result on these drugs should be doubled before it is trusted.
Why PSA is low
A low PSA is generally reassuring — the lower the level, the lower the statistical chance of prostate cancer — which is why the high direction matters more. Still, a low number is worth understanding, roughly by frequency:
- A small, healthy prostate — the usual, benign explanation, common in younger men.
- 5-alpha-reductase inhibitors — finasteride and dutasteride, taken for an enlarged prostate or hair loss, roughly halve PSA within months, so a low reading on them is doubled for interpretation.
- Obesity — a larger blood volume dilutes PSA and can mask a significant cancer in men with a high BMI.
- Some medicines — statins, thiazide diuretics and long-term NSAIDs can lower it modestly.
One limit: a low PSA does not fully rule out cancer, because a minority of aggressive, poorly differentiated tumors make little of it. After surgery to remove the prostate, PSA should instead fall to undetectable (under 0.1 ng/mL); any later rise is the earliest signal the cancer has returned.
What to test alongside
PSA is read with a few refinements and, when needed, the rest of the panel:
- Free PSA (% free PSA) — the unbound share; a low percentage in the 4–10 ng/mL “gray zone” raises suspicion of cancer and can spare an unnecessary biopsy.
- Creatinine — kidney function, checked when an enlarged prostate blocks urine flow or before imaging with contrast dye.
- The other markers in this tumor-marker panel, each tied to a different organ: CEA (bowel and other cancers), AFP (liver and testicular), CA 19-9 (pancreas), CA 125 and HE4 (ovary), and CA 15-3 (breast).
An abnormal PSA is now usually followed by a multiparametric MRI of the prostate before any biopsy decision.
What to do about an abnormal result
- Don’t panic — and don’t self-treat. Most raised PSA results are not cancer, and no supplement safely lowers a meaningful PSA.
- Remove the confounders, then repeat. Avoid ejaculation and hard cycling for about 48 hours before the draw, and wait several weeks after a urine infection or biopsy; a single abnormal value is confirmed with a repeat.
- Tell your doctor your medicines. Finasteride and dutasteride roughly halve PSA, so flag them — the true value is about double what the lab shows.
- See your primary-care doctor first. They repeat the test, examine the prostate and, if the result stands, refer you to a urologist.
- Follow the specialist pathway. A urologist weighs your % free PSA, PSA density and trend and considers biopsy only if the risk warrants it, in line with NICE guidance.
- Decide about screening deliberately. Whether to test at all is a shared decision: the USPSTF calls PSA screening an individual choice for men aged 55–69 and advises against it from 70.
Mini-FAQ
What is a normal PSA level?
There is no single cutoff. A total PSA under 4.0 ng/mL is the traditional normal, but many labs use lower age-adjusted limits — roughly 2.5 in your 40s rising to about 6.5 in your 70s. It is a sliding scale of risk, not a pass-or-fail line.
Does a high PSA mean I have prostate cancer?
No. Most raised results come from a benign enlarged prostate, prostatitis, a urine infection or recent activity such as cycling or ejaculation. Only a minority turn out to be cancer, though the odds climb as the number rises.
What can falsely raise or lower a PSA result?
Ejaculation, hard cycling, a recent catheter, a prostate biopsy or an infection can push PSA up for days to weeks. Finasteride and dutasteride (for an enlarged prostate or hair loss) roughly halve it, and obesity lowers it modestly — so tell your doctor if this applies.
Should I have a PSA test?
For men aged 55–69 the USPSTF calls it an individual decision made with your doctor, weighing earlier cancer detection against the risk of over-diagnosis; routine screening is not advised from age 70. Discuss your own risk before deciding.
What PSA level is checked after prostate cancer treatment?
After the prostate is surgically removed, PSA should fall to undetectable — under 0.1 ng/mL. A PSA that rises on repeat testing is the earliest sign the cancer has returned, which is why it is tracked for years afterwards.
