Overview
Quality control in clinical chemistry uses control materials and statistical rules to detect analytical error before patient results are released.
Classification
| Rule (examples) | Pattern | Typical meaning |
|---|---|---|
| 1-3s | 1 point >3 SD | Random or large systematic error, reject |
| 2-2s | 2 consecutive >2 SD same side | Systematic shift |
| R-4s | Range of 4 SD within run | Random error |
| 4-1s / 10x | Trend/shift patterns | Developing systematic error |
Morphologic Features
QC statistics reference, not morphologic.
Laboratory Characteristics
- Assay-specific means and SDs
- Documented corrective actions
- Scheduled QC frequency per SOP/regulator expectations
Reference Intervals
QC ranges are not patient reference intervals. Do not confuse control limits with clinical decision limits.
Clinical and Laboratory Significance
Effective QC prevents clinically misleading chemistry results from analytical drift or imprecision.
Differential Considerations
Differentiate reagent failure, calibration error, instrument fault, and control-material mishandling when QC fails.
Comparison Tables
Calibration vs QC
| Item | Calibration | QC |
|---|---|---|
| Primary purpose | Set response | Monitor control |
| Material | Calibrators | Controls |
| Frequency driver | Lot/maintenance/schedule | Shift/run schedule + events |
Classification Frameworks
Not applicable.
Laboratory Notes
- Follow local Westgard configuration exactly
- Never “test until pass” without investigation
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 8th ed. Elsevier; 2022.
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Bishop ML, Fody EP, Schoeff LE. Clinical Chemistry: Principles, Techniques, and Correlations. 9th ed. Jones & Bartlett; 2022.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Collection of Diagnostic Venous Blood Specimens. CLSI standard GP41. CLSI.
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