Single-Breath Diffusing Capacity for Carbon Monoxide Instrument Accuracy Across 3 Health Systems

BACKGROUND: Measuring diffusing capacity of the lung for carbon monoxide (D-LCO) is complex and associated with wide intra- and inter-laboratory variability. Increased D-LCO variability may have important clinical consequences. The objective of the study was to assess instrument performance across hospital pulmonary function testing laboratories using a D-LCO simulator that produces precise and repeatable D-LCO values. METHODS: D-LCO instruments were tested with CO gas concentrations representing medium and high range D-LCO values. The absolute difference between observed and target D-LCO value was used to determine measurement accuracy; accuracy was defined as an average deviation from the target value of <2.0 mL/min/mm Hg. Accuracy of inspired volume measurement and gas sensors were also determined. RESULTS: Twenty-three instruments were tested across 3 healthcare systems. The mean absolute deviation from the target value was 1.80 mL/min/mm Hg (range 0.24-4.23) with 10 of 23 instruments (43%) being inaccurate. High volume laboratories performed better than low volume laboratories, although the difference was not significant. There was no significant difference among the instruments by manufacturers. Inspired volume was not accurate in 48% of devices; mean absolute deviation from target value was 3.7%. Instrument gas analyzers performed adequately in all instruments. CONCLUSIONS: D-LCO instrument accuracy was unacceptable in 43% of devices. Instrument inaccuracy can be primarily attributed to errors in inspired volume measurement and not gas analyzer performance. D-LCO instrument performance may be improved by regular testing with a simulator. Caution should be used when comparing D-LCO results reported from different laboratories.