Standardization of prostate-specific antigen assays: Impact on reference intervals and clinical decision thresholds

BackgroundProstate-specific antigen (PSA) remains the most widely used biomarker for prostate cancer screening, diagnosis, and monitoring. However, despite decades of standardization efforts, significant inter-assay variability persists, with important consequences for clinical interpretation and decision-making.ObjectiveThis review aims to evaluate the impact of PSA calibration and harmonization on reference intervals, clinical thresholds, and population-based screening strategies in contemporary clinical practice.MethodsA literature-based analysis was conducted, examining studies on PSA assay standardization, analytical variability, and evidence from population screening trials, including considerations from a Health Technology Assessment perspective.ResultsThe introduction of the World Health Organization (WHO) International Standard 96/670 improved comparability among PSA assays, yet clinically relevant differences between platforms remain. This variability is driven by differences in calibration, antibody specificity, epitope recognition, and assay design. As a result, PSA values are not directly interchangeable across assays, and assay-specific cut-offs may be necessary to maintain diagnostic performance. Historically established thresholds, such as the 4 μg/L cut-off and the "gray zone," were derived using specific assay systems and are influenced by methodological limitations. PSA-derived metrics, including PSA density, improve specificity but are still affected by inter-assay variability. Evidence from large randomized trials supports a PSA cut-off of 3.0 μg/L for population screening, showing a reduction in prostate cancer mortality when implemented within structured programs; however, this threshold is intrinsically linked to the analytical characteristics of the assays used. PSA also shows relevant intra-individual biological variability beyond analytical variation, with within-subject variation of 6-13%.ConclusionsPSA standardization remains incomplete, and inter-assay variability and biological variability continues to influence clinical interpretation. The implementation of PSA-based screening programs must explicitly consider the assay-specific nature of evidence-derived thresholds, including the 3.0 μg/L cut-off, to ensure consistent, effective, and safe clinical decision-making.