BACKGROUND:The 2017 American Thoracic Society/European Respiratory Society (ATS/ERS) diffusing capacity of the lung for carbon monoxide (D LCO ) standards specify a control rule for assessing biologic quality control (BioQC) but have limited guidance on how to establish expected values for control rule variables. This study aimed to determine expected values for D LCO BioQC using coefficient of variation (CV) and compare that the mean 6 2 SD control rule yields the same precision as mean 6 12% of the mean. METHODS: D LCO BioQC data were collected from a multi-center inhaled medication study. This descriptive study spanned 42 months ending in 2018. The annual D LCO CV was based upon 10 D LCO values separated by at least 5 d. The root mean square CV (RMSCV) was computed for each year and Friedman test evaluated within subject annual CV changes. Ninetieth percentile values were computed for annual control rule limits/mean D LCO . RESULTS: Of 217 BioQCs, the study's first year had 168 subjects with fewer in subsequent years. Annual CV values from RMSCV were 5.3, 4.5, and 4.6% in years 1, 2, and 3, respectively. No change was seen in the CV for those subjects with data for all 3 years, n 5 24, P 5 .07. The 90th percentile of measurements 2 SD/mean D LCO were 15, 12.4, and 11% in years 1, 2, and 3, respectively. CONCLUSIONS: A D LCO BioQC CV ^6% is achievable across multiple sites, technologists, and brands of equipment. This CV value assures that measurements for control rule variables emerge from an expected range. A control rule of mean 6 2 SD appeared to yield similar results as the mean 6 12% of the mean rule reported in the 2017 ATS/ERS D LCO standards.
BACKGROUND: Although quality control standards are recommended to ensure accurate test results, the coefficient of variation for the FVC and FEV 1 biologic quality control (BioQC) is not specified. The primary aim of this study was to evaluate variations in spirometry BioQCs in a large and diverse cohort of individuals to determine an acceptable standard for the coefficient of variation. METHODS: The FVC and FEV 1 biologic control data were secondary analyses from an inhaled medication trial that was conducted over 3 y ending in 2018 that included 114 laboratories. Results were sent to a central repository for expert review. The FVC and FEV 1 coefficients of variation were based upon a minimum of 10 spirometry values annually separated by at least 5 d. A second method of computing the coefficient of variation used 10 values within 28 d. Descriptive statistics were computed. Wilcoxon signed-rank tests were conducted to compare whether the median coefficient of variation values between the 2 methods differed, tested at a 5 0.05 using SPSS. RESULTS: Of 249 biologic control participants, 170 met the first year's inclusion criteria. The coefficient of variation for the 5-d separated method was < 5% for 94.1% of FVC and 93.5% of FEV 1 values in the first year. By year 3, 90% of FVC and FEV 1 coefficient of variation values were < 4%. The medians for the 5-d separated and the 28-d measure showed no difference for either FVC coefficient of variation or FEV 1 coefficient of variation, Z 5 21.764, P 5 .78, and Z 5 20.980, P 5 .33, respectively. CONCLUSIONS: Interlab biologic control variation values of < 4% for FVC and FEV 1 are achievable; however, individual labs should strive to attain lower values. Acceptable coefficients of variation can be achieved within 28 d.
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