Tumor markers
Prostate-specific antigenPSA
Glycoprotein from prostate epithelium; screening, surveillance, and post-treatment monitoring.
Sample
Serum
Clinical reference range
— to 4 ng/mL
Age-adjusted · 40s <2.5, 50s <3.5, 60s <4.5, 70s <6.5
Conv: —–4 ng/mL
Biology
What it measures
Serine protease that liquefies semen. Tissue-specific (not cancer-specific) — produced by both benign and malignant prostate tissue.
Clinical use
Why we order it
Shared decision screening 55–69 (USPSTF grade C). Surveillance after prostatectomy/radiation.
Lens · Clinical
Interpretation by lens
Clinical interpretation
After radical prostatectomy, PSA >0.2 ng/mL on two consecutive draws defines biochemical recurrence (AUA).
Differential
Causes of abnormal values
Causes of HIGH
- ↑Prostate cancer
- ↑BPH
- ↑Prostatitis
- ↑Recent ejaculation/DRE/cycling
- ↑UTI
- ↑Urinary retention
Pitfalls
Pre-analytic & interpretation traps
- !5α-reductase inhibitors (finasteride, dutasteride) halve PSA — double the measured value when interpreting.
- !Use PSA velocity, density, and free/total ratio to refine — free PSA <10% raises cancer probability.
- !Post-prostatectomy PSA should be undetectable; any rise = biochemical recurrence.
Evidence-graded claims
What the data says
B
PSA screening reduces prostate cancer-specific mortality.
ERSPC: NNS ~570 to prevent one death over 16 y; absolute benefit modest, harms (overdiagnosis) substantial.
B
PSA density (PSA / prostate volume) outperforms total PSA for biopsy decisions.
Useful >0.15 ng/mL/cc threshold.