Laboratory Operations and Quality Management
Core concepts
Quality management spans preanalytical, analytical, and postanalytical phases. Distinguish quality control (daily monitoring of a method with control materials) from quality assurance (the broader system: SOPs, competency assessment, proficiency testing, audits, corrective action). Know Levey-Jennings charts and Westgard rules (1-2s as a warning, 1-3s rejection, 2-2s, R-4s, 4-1s, 10x), calibration versus calibration verification, and method validation versus verification. Understand accuracy (closeness to truth) versus precision (reproducibility), random versus systematic error, and why sensitivity and specificity differ from positive and negative predictive value, which depend on prevalence.
Traps
- A shift is a sudden systematic change and a trend is a gradual drift; both point to an assignable cause, not random error.
- Delta checks and critical value reporting are postanalytical safety nets, not substitutes for analytical QC.
- Proficiency testing failures require root cause investigation, not simply re-testing the sample.
- Biosafety levels and chemical hygiene plans appear in questions about spill response, waste handling, and personnel training.
Worked example
A chemistry control reads +2.6 SD on one level and +2.8 SD on another. A single result beyond 2 SD is only a 1-2s warning; when both levels exceed +2 SD on the same side, the 2-2s rule rejects the run. Investigate a systematic shift, such as a new reagent lot or calibration drift, before reporting patient results.