Assay Standardization Bias: Different Prostate Cancer Detection Rates and Clinical Outcomes Resulting from Different Assays for Free and Total Prostate-Specific Antigen

Using a free/total PSA ratio of 20% or less as the threshold for biopsy, the differences in assay sensitivity and specificity for detecting prostate cancer are significant. Commercially available assays for PSA and its derivatives are not necessarily interchangeable, and these differences might lead to different clinical outcomes. When using free and total PSA measurements to make clinical decisions, patients and physicians should be aware of the potential standardization bias and which assay is being used.