PSA Standardization

Effect of Analytical Bias on Classification Based on Fixed Criteria

October 2009

If we simply examine the effect of analytical bias alone on classification that is based on a fixed criteria, it may be more obvious what this means. Let’s say these curves represent a distribution of patients who have their PSA measured. On the right side of the curve we have our fixed decision threshold (in this case we’ll use 4.0 ng/mL) and the marked area represents our patients with a disease (prostate cancer) we want to detect.  If we have an analytical shift in the calibration then we move the curve to the left by 20%.  If the cutoff does not shift to match the lower patient results, then the number of patients we detect simply decreases. This, in a very simplistic explanation, is what we see between Hybritech and WHO assays if the cutoff does not change.

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• Introduction
• Elevated PSA Result on Screening
• Reasons for Ordering PSA¹
• PSA Screening in the News
• Recommendations for Screening
• Arguments for Screening for Prostate Cancer
• Recommendations for Not Screening
• Arguments Against Screening for Prostate Cancer
• PSA Sensitivity and Specificity
• High-Grade Prostate Cancer is Not Rare When PSA =4.0 ng/mL⁶
• Increase Specificity Using PSA Velocity⁸
• Optimizing Clinical Sensitivity and Specificity: Age/Ethnic Reference Intervals^9,10
• Utilization of Free/Total PSA Ratio¹¹
• Why Aren't PSA Results Interchangeable?
• Development of PSA Standards
• Development of PSA Standards
• Effect of Analytical Bias on Classification Based on Fixed Criteria
• Analytical Difference: Results per 1000 Patients Tested¹³
• Hybritech vs. WHO Standardized Assays^12,14
• Analytical Differences¹⁵
• CAP Proficiency Testing
• WHO 96/670 Total PSA Preparations¹⁶
• WHO Calibration/Concordance at 3.1 ng/mL Cutoff⁵
• WHO Calibration/Concordance at 3.1 ng/mL Cutoff⁵
• WHO Calibration/Concordance at 4.0 ng/mL Cutoff⁵
• Clinical Differences in PSA Screening¹⁴
• The Clinical Difference
• Fixed Thresholds Produce Problems for Biopsy Recommendations
• Effect on "Watchful Waiting"
• Effect on "Watchful Waiting"
• Adding Biological Variability into the Mix
• Futures in Prostate Cancer Testing?
• PSA Testing at Mayo
• Conclusions
• References
• References
• Questions?