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Clinical Chemistry 53: 575-580, 2007. First published February 22, 2007; 10.1373/clinchem.2006.083311
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(Clinical Chemistry. 2007;53:575-580.)
© 2007 American Association for Clinical Chemistry, Inc.

Current Issues in Laboratory Medicine

Evaluation of the Performance of Randomized versus Fixed Time Schedules for Quality Control Procedures

Curtis A. Parvin1 and Sanford Robbins, III2,a

1 Department of Pathology and Immunology, Washington University School of Medicine, Saint Louis, MO.
2 Department of Pathology, Anne Arundel Medical Center, 2001 Medical Parkway, Annapolis, MD.

aAddress correspondence to this author at: Department of Pathology, Anne Arundel Medical Center, 2001 Medical Pkwy., Annapolis, MD 21401. Fax 443-481-4207; e-mail srobbins{at}aahs.org.

Background: Although minimum regulatory standards exist for determining QC testing frequency, decisions regarding when and how to run QC samples are not standardized. Most QC testing strategies test control samples at fixed time intervals, often placing the samples in the same position on an instrument during subsequent QC events and leaving large gaps of time when control samples are never run, yet patient samples are being tested.

Methods: Mathematical derivations and computer simulation were used to determine the expected waiting time between an out-of-control condition and the next scheduled QC test for various QC testing strategies that use fixed or random intervals between QC tests.

Results: Scheduling QC tests at fixed intervals yields an average time between the occurrence of an out-of-control error condition and the next scheduled QC test that is equal to half of the fixed time interval. This performance was the best among the QC scheduling strategies investigated. Near-optimal performance, however, was achieved by randomly selecting time intervals between QC events centered on the desired expected interval length, a method that provides variation in QC testing times throughout the day.

Conclusions: If the goal is to vary QC testing times throughout the day while maintaining the shortest expected length of time between error conditions and the next scheduled QC test, then a near-optimal QC scheduling strategy combines randomly selected time intervals centered on the desired length of time between QC events with fixed time intervals.






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Copyright © 2007 by the American Association for Clinical Chemistry.