What is a PSA test and how accurate is it?

The PSA test measures a prostate-produced protein in your blood. At a standard threshold of ≥4.0 ng/mL, it has a sensitivity of roughly 70–80% (meaning it misses around 1 in 5 cancers) and a specificity of around 60–70%. Only about 25–40% of men who go on to biopsy after an elevated PSA are found to have cancer. It is best understood as a triage signal – useful for flagging risk, but not a diagnosis in itself. Combined with multiparametric MRI, its predictive value improves substantially.