Laboratory Operations / Quality Management
Laboratory Operations / Quality Management
This domain tests quality control rules, method validation, and regulatory documentation - the system that proves a reported result is trustworthy.
Core rules
- Levey-Jennings charts plot QC values against established mean and SD; Westgard rules define rejection. 1-2s is a warning; 1-3s, 2-2s, R-4s, 4-1s, and 10x are rejection rules.
- Calibration establishes the relationship between signal and concentration using calibrators; verification confirms performance claims (accuracy, precision, reportable range) before patient testing.
- Proficiency testing must be handled as routine patient samples, without sharing results between laboratories.
- Delta checks compare a result with the patient's previous value; a change exceeding a defined limit triggers review for specimen mix-up or mislabeling.
- Six Sigma metrics combine bias, CV, and allowable total error to estimate error rate; higher sigma means fewer defects.
Worked example
A chemistry analyte has a mean of 100 mg/dL and SD of 2. Two consecutive QC results are 104 and 105 mg/dL (+2.0s and +2.5s). The 2-2s rule is violated even though neither exceeds 3s, so the run is rejected. Investigation finds a deteriorating reagent lot; recalibration and reanalysis of patient samples from that period are required. Accepting the run because no single point exceeded 3s is the classic error.
Traps that cost marks
- Treating 1-2s as a rejection rule rather than a warning.
- Using QC results from a different lot or level to judge a run.
- Reporting patient results before investigating a rejected run.
- Failing to document corrective action, which is what an inspector reviews.