A Patient Based Approach to Doing the Right QC
Instead of a regulatory minimum frequency for running controls, Clinical and Laboratory Standards Institute (CLSI) expresses a patient based approach in Standard C24 “Statistical Quality Control for Quantitative Measurement Procedures: Principles and Definitions; Approved Guideline.” According to CLSI, “The user should determine the location of control samples within a run, keeping in mind the principle that quality control results should be evaluated before reporting patient samples from the run.”
- The location of control samples should consider the type of analytical process, the kind of errors that might occur, and the protocol for reporting patient results. For example, if an analytical run corresponds to a discrete batch of samples, controls might be located at the beginning and end of the run to detect shifts, might be spaced evenly throughout the batch to monitor drift, or distributed randomly among patient samples to detect errors. In any case, the QC results would be evaluated before patient results were reported.
- For a high-volume analyzer that continuously produces test results, an appropriate analytical run might be defined as a certain interval of time, then QC samples would be analyzed and evaluated at the beginning of a run and then as each run (i.e., the next time interval or defined number of samples) occurs.
- If a quality control fault is detected, results reported since the previous quality control event should be reviewed.6
CLIA mandates corrective action for all patient test results in the unacceptable test run. For example, when any of the following occur:
- Results of control or calibration materials, or both, fail to meet the laboratory's established criteria for acceptability.
- All patient test results obtained in the unacceptable test run and since the last acceptable test run must be evaluated to determine if patient test results have been adversely affected. The laboratory must take the corrective action necessary to ensure the reporting of accurate and reliable patient test results. 7
6 Clinical and Laboratory Standards Institute, C24 Statistical Quality Control for Quantitative Measurement Procedures: Principles and Definitions, Wayne PA. Section 8.3 Location of Control Samples.