Laboratory Quality Control Based on Risk Management
CLSI adds to the C24 principle that quality control results should be evaluated before reporting patient samples from the run in EP23-A "Laboratory Quality Control Based on Risk Management; Approved Guideline," which expressly addresses the optimal frequency of QC material testing with respect to risk assessment. In section 5.1.6 of EP-23, CLSI states:
- The optimal frequency of performing QC sample procedures depends on built-in and other controls for a given measuring system, the stability of that measuring system, and conditions in the laboratory identified through risk assessment that could affect the reliability of testing such as staff turnover, and the clinical risk of harm to a patient if an erroneous result is reported and acted on. The frequency of control procedures should also conform to applicable regulatory and accreditation requirements.
CLSI emphasizes the advantages of testing QC materials at shorter intervals:
- Monitoring the measuring system at shorter intervals increases the likelihood that systematic errors are detected before incorrect results are reported, or decreases the time before alerting the health care provider who may have received incorrect results. For example, a laboratory that evaluates the examination (analytical) process every eight hours will identify a systematic error condition much earlier than a laboratory that monitors the examination process every 24 hours. However, the total number of specimens tested in a time interval may also influence the frequency of monitoring. For example, a laboratory that tests 2000 samples in one 24-hour period might perform control procedures several times a day, whereas a laboratory that tests 50 samples in an eight-hour shift might perform control procedures at the beginning and end of a shift. The complex relationship between the frequency of QC sample testing, frequency of false rejection, and the quality of patient results has been explored by Parvin and colleagues.8
In discussing EP23-A, James Nichols, PhD, chair of the subcommittee that developed the guideline, commented:
The [CLIA] requirement for testing two levels of liquid QC every day a test is run comes from the days when labs ran just a few batches of patient samples a day. With the new, more automated analyzers, there is no longer batch analysis and patient samples are run continuously. So now, the question is, do we hold those samples until the next QC run, or do we run QC continuously, every 10, 20, or 50 samples and release results in small batches? These operational considerations lead to turnaround time issues, cost issues and resource issues.9
Running QC continuously every 10, 20, or 50 samples and releasing results in small batches is a bracketed QC strategy.
8 Clinical and Laboratory Standards Institute, EP23-A Laboratory Quality Control Based on Risk Management; Approved Guideline, Wayne PA. Section 5.1.6 Frequency of Quality Control Sample Testing.
9 Malone, B. "A New Approach to Quality Control. How Can Risk Management Help Labs?" Clinical Laboratory News, November 2011, Volume 37, No 11.