How does proficiency testing influence method comparison and improvement in laboratory QC?

• A. It eliminates the need for internal QC
• B. It focuses only on cost comparisons
• C. It replaces proficiency testing with internal QC
• D. It identifies performance gaps and biases by comparing across labs, prompting corrective actions and method optimization

Answer: (D)

Proficiency testing provides external benchmarks by comparing a lab’s results with those of peer laboratories using the same or similar methods. This setup helps uncover performance gaps and biases that internal QC alone might miss, since it shows how a lab stacks up against others in real-world practice. When discrepancies emerge, the lab can investigate possible sources—calibration, reagent lots, instrument performance, or data interpretation—and take corrective actions. Those actions often lead to method optimization, adjustments to QC rules, or even method changes to improve accuracy and consistency. Proficiency testing adds valuable external context to internal QC and guides improvement without replacing internal QC or focusing on costs.