Quality Control and Quality Management
Quality management spans the total testing process: preanalytic, analytic, and postanalytic phases. Know the elements of a quality management system-document control, competency, equipment maintenance, occurrence management, and continuous improvement.
Statistical QC: establish control means and SDs from at least 20 data points under stable conditions. Apply Westgard multirules: 1-2s is a warning; 1-3s, 2-2s, R-4s, 4-1s, and 10x are rejection rules. Distinguish random error (1-3s, R-4s) from systematic error (2-2s, 4-1s, 10x). Understand that a shift is a sudden change in mean and a trend is a gradual drift.
Other QC concepts: proficiency testing performance, method validation, calibration verification, and the use of patient-based QC (moving averages, delta checks). Understand the difference between internal QC and external quality assessment. Know sigma metrics and the relationship between allowable total error, bias, and imprecision; six-sigma processes need less frequent QC.
Regulatory requirements: documented corrective action when QC fails, review of QC by the director, and retention of records. Root cause analysis and failure mode effects analysis are quality improvement tools.
Worked example: a control exceeds +2 SD on two consecutive runs (2-2s rule). This indicates systematic error; investigate calibration, reagent lot change, or deterioration before reporting patient results.
Trap: treating a 1-2s warning as automatic rejection-it is a warning only unless accompanied by another rule violation.