Singapore Institute of Technology

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Between and within calibration variation: implications for internal quality control rules

journal contribution
posted on 2023-02-23, 08:17 authored by Chun Yee LimChun Yee Lim, Jermyn Jit Siong Lee, Kay Weng ChoyKay Weng Choy, Tony Badrick, Corey MarkusCorey Markus, Tze Ping LohTze Ping Loh

The variability between calibrations can be larger than the within calibration variation for some measurement procedures, that is a large CVbetween:CVwithin ratio. In this study, we examined the false rejection rate and probability of bias detection of quality control (QC) rules at varying calibration CVbetween:CVwithin ratios.

Historical QC data for six representative routine clinical chemistry serum measurement procedures (calcium, creatinine, aspartate aminotransferase, thyrotrophin, prostate specific antigen and gentamicin) were extracted to derive the CVbetween:CVwithin ratios using analysis of variance. Additionally, the false rejection rate and probability of bias detection of three ‘Westgard’ QC rules (2:2S, 4:1S, 10X) at varying CVbetween:CVwithin ratios (0.1–10), magnitudes of bias, and QC events per calibration (5–80) were examined through simulation modelling.

The CVbetween:CVwithin ratios for the six routine measurement procedures ranged from 1.1 to 34.5. With ratios >3, false rejection rates were generally above 10%. Similarly for QC rules involving a greater number of consecutive results, false rejection rates increased with increasing ratios, while all rules achieved maximum bias detection.

Laboratories should avoid the 2:2S, 4:1S and 10X QC rules when calibration CVbetween:CVwithin ratios are elevated, particularly for those measurement procedures with a higher number of QC events per calibration.


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