What is the purpose of proficiency testing (PT) in a drug testing laboratory?

• A. To externally evaluate a lab's performance using blinded samples and ensure accuracy and comparability across laboratories.
• B. For internal QA of equipment only
• C. For staff training and certification
• D. For auditing building facilities

Answer: (A)

Proficiency testing serves as an external quality check that measures how well a drug testing lab performs its tasks by using blinded samples with known results. The lab analyzes these samples just as it would routine cases, and the results are compared against those from other laboratories. This external benchmarking reveals how accurately and consistently the lab reports findings and helps uncover biases, systematic errors, or drift in methods. It supports accreditation and regulatory expectations by demonstrating that results are comparable across laboratories, not just within one facility. Internal quality assurance focuses on the lab’s own processes and equipment, staff training ensures competence, and facilities audits review infrastructure—yet proficiency testing provides the external performance evaluation across labs, which is why it’s the best fit.