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Antimicrobial Agents and Chemotherapy, July 2007, p. 2483-2488, Vol. 51, No. 7
0066-4804/07/$08.00+0     doi:10.1128/AAC.01457-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Statistical Methods for Establishing Quality Control Ranges for Antibacterial Agents in Clinical and Laboratory Standards Institute Susceptibility Testing{triangledown}

John Turnidge1* and Gerry Bordash2

Division of Laboratory Medicine, Women's and Children's Hospital, North Adelaide, Australia,1 Dade Behring—MicroScan, West Sacramento, California2

Received 20 November 2006/ Returned for modification 23 January 2007/ Accepted 9 April 2007

Quality control (QC) ranges for antimicrobial agents against QC strains for both dilution and disk diffusion testing are currently set by the Clinical and Laboratory Standards Institute (CLSI), using data gathered in predefined structured multilaboratory studies, so-called tier 2 studies. The ranges are finally selected by the relevant CLSI subcommittee, based largely on visual inspection and a few simple rules. We have developed statistical methods for analyzing the data from tier 2 studies and applied them to QC strain-antimicrobial agent combinations from 178 dilution testing data sets and 48 disk diffusion data sets, including a method for identifying possible outlier data from individual laboratories. The methods are based on the fact that dilution testing MIC data were log normally distributed and disk diffusion zone diameter data were normally distributed. For dilution testing, compared to QC ranges actually set by CLSI, calculated ranges were identical in 68% of cases, narrower in 7% of cases, and wider in 14% of cases. For disk diffusion testing, calculated ranges were identical to CLSI ranges in 33% of cases, narrower in 8% of cases, and 1 to 2 mm wider in 58% of cases. Possible outliers were detected in 8% of diffusion test data but none of the disk diffusion data. Application of statistical techniques to the analysis of QC tier 2 data and the setting of QC ranges is relatively simple to perform on spreadsheets, and the output enhances the current CLSI methods for setting of QC ranges.

* Corresponding author. Mailing address: Division of Laboratory Medicine, Women's and Children's Hospital, 72 King William Rd., North Adelaide, South Australia 5006, Australia. Phone: 61 8 81616873. Fax: 61 8 81616189. E-mail: john.turnidge{at}cywhs.sa.gov.au

{triangledown} Published ahead of print on 16 April 2007.

Antimicrobial Agents and Chemotherapy, July 2007, p. 2483-2488, Vol. 51, No. 7
0066-4804/07/$08.00+0     doi:10.1128/AAC.01457-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Turnidge, J., Paterson, D. L. (2007). Setting and Revising Antibacterial Susceptibility Breakpoints. Clin. Microbiol. Rev. 20: 391-408 [Abstract] [Full Text]  


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