Lab Med Online.  2012 Oct;2(4):183-187.

Should I Repeat My 1:2s QC Rejection?

• Parvin CA
• Kuchipudi
• Yundt-Pacheco JC

Abstract

BACKGROUND
Repeating a QC that is outside 2SD from the mean (1:2s rule) appears to be a common practice. Although this form of repeat-sampling is frowned on by many, the comparative power of the approach has not been formally evaluated.
METHODS
We computed power functions mathematically and by computer simulation for 4 different 1:2s repeat-sampling strategies, as well as the 1:2s rule, the 1:3s rule, and 2 common QC multirules.
RESULTS
The false-rejection rates for the repeat-sampling strategies were similarly low to those of the 1:3s QC rule. The error detection rates for the repeat-sampling strategies approached those of the 1:2s QC rule for moderate to large out-of-control error conditions. In most cases, the power of the repeat-sampling strategies was superior to the power of the QC multirules we evaluated. The increase in QC utilization rate ranged from 4% to 13% for the repeat-sampling strategies investigated.
CONCLUSIONS
The repeat-sampling strategies provide an effective tactic to take advantage of the desirable properties of both the 1:2s and 1:3s QC rules. Additionally, the power of the repeat-sampling strategies compares favorably with the power of 2 common QC multirules. These improvements come with a modest increase in the average number of controls tested.

MeSH Terms

Computer Simulation
Imidazoles
Nitro Compounds
Imidazoles
Nitro Compounds

Figure

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  Fig. 1 Power function curves for the 4 repeat sampling strategies described in Table 1 compared to a 1:2s QC rule, a 1:3s QC rule, and a 1:3s/2:2s/R:4s multirule when 2 concentration levels of control material are examined.

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  Fig. 2 Power function curves for the 4 repeat sampling strategies described in Table 1 compared to a 1:2s QC rule, a 1:3s QC rule, and a 1:3s/2of3:2s/R:4s multirule when 3 concentration levels of control material are examined.

Reference

1. International Organization for Standardization (ISO). ISO 15189. Medical laboratories: particular requirements for quality and competence. 2007. Geneva: ISO.

2. Housley D, Kearney E, English E, Smith N, Teal T. Audit of internal quality control practice and processes in the south-east of England and suggested regional standards. Ann Clin Biochem. 2008. 45:135–139.

3. Westgard JO. Assuring the right quality right. 2007. Madison (WI): Westgard QC.

4. Cembrowski GS, Carey RN. Laboratory quality management: QC & QA. 1989. Chicago: ASCP Press.

5. Daudin JJ. Double sampling X_charts. J Qual Technol. 1992. 24:78–87.