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Quality control practices for calcium, cholesterol, digoxin, and hemoglobin: a College of American Pathologists
1Centers for Disease Control and Prevention, Public Health Practice Program Office, Division of Laboratory Systems, Laboratory Performance Assessment Branch, Chamblee, GA, USA.
Objective:
To assess quality control (QC) practices and their impact on hospital laboratories using the College of American Pathologists (CAP) Q-Probes process.
Design:
Self-directed data gathering, using a questionnaire to determine QC practices, data input forms for 6 months retrospective quality control use and run failure rates, and input forms for 3 months prospective data concerning QC failure rates and corrective steps taken. Participants submitted data for four analytes: calcium, cholesterol, digoxin, and hemoglobin.
Participants:
Laboratories enrolled in the 1994 CAP Q-Probes program.
Main Outcome Measures:
Retrospective and prospective QC failure rates compared with QC protocols and the corrective steps.
Results:
Five hundred five hospital laboratories returned various components of the study. Median retrospective run rejection rates per 1000 runs: calcium, 4.3; cholesterol, 3.6; digoxin, 4.3; and hemoglobin, 2.4. Corresponding median prospective run rejection rates per 1000 runs: calcium, 5.8; cholesterol, 5.6; digoxin, 6.5; and hemoglobin, 3.6. Participants resolved most out-of-control events in less than 20 minutes, with no patient samples repeated. More than 95% of the time, participants resolved out-of-control events simply by repeating controls. Most participants used a single control rule based on a target mean plus or minus a multiple of the standard deviation. A few laboratories used multirule systems.
Conclusions:
Current testing methods yield few out-of-control events, which usually are resolved rapidly, with little impact on laboratory operation. We recommend modification and simplification of laboratory QC practices to decrease false rejection rates and to use modern instrumentation more efficiently.