Laboratory Responsibility for QC
Regulations under Clinical Laboratory Improvement Amendments (CLIA) state the laboratory is responsible for having control procedures that monitor the accuracy and precision of the complete analytic process. The laboratory must establish the number, type and frequency of testing control materials. The control procedures must:
- Detect immediate errors; and,
- Monitor over time the accuracy and precision of test performance.
CLIA then mandates the legal minimum frequency and number of levels:
- At least once each day patient specimens are assayed . . . include two control materials of different concentrations.4
While running two control materials of different concentrations may meet minimum regulatory requirements, it may not fully address the need to control either the measurement range or the reportable range. Two levels may not be enough to provide adequate quality control across clinical decision levels and the expected measurement range. "Concurrently using quality control samples at multiple levels, allows application of additional quality control rules that improve detection and interpretation of analytical error (i.e. proportional vs. constant, random vs. systematic)."5 For more information on including enough levels see the related article Concentrations of Control Materials.
Again, while running QC materials just once each day may meet minimum regulatory requirements it may not be often enough to ensure that patient samples are reported with confidence. Running QC materials just once each day can open a window of vulnerability where erroneous patient results are reported before QC materials are run and QC data reviewed. For more information on the window of vulnerability see the related article Expected Number of Patients Compromised by Failure.
5 Clinical and Laboratory Standards Institute, C24 Statistical Quality Control for Quantitative Measurement Procedures: Principles and Definitions, Wayne PA. Section 6.2.2 Concentrations of Analytes in Control Materials.