D_LCO Biologic Quality-Control Findings From a Multi-Center Global Study

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 ± 2 SD control rule yields the same precision as mean ± 12% of the mean.

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.

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 = 24, P = .07. The 90th percentile of measurements 2 SD/mean D_LCO were 15, 12.4, and 11% in years 1, 2, and 3, respectively.

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 ± 2 SD appeared to yield similar results as the mean ± 12% of the mean rule reported in the 2017 ATS/ERS D_LCO standards.