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

Abstract

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.

DLCOBiologic Quality-Control Findings From a Multi-Center Global Study

“…19 In another study of 15 PFLs, most did not have standardized BioQC procedures, and initially 43% of the machines had unacceptable accuracy. 20 Technologists need to utilize principles of measurement science in their QC practices. The CLSI (https://clsi.org/.…”

“…Methods for decreasing variability in D LCO have been reported in multiple studies. These include using a D LCO simulator, 6,17,20,21 same brand of PFT equipment, 6,7,9,22 standardizing test protocols, 9,10,22 providing staff education with a written test and return demonstration, 9,10,22 and review of D LCO results at a centralized site with feedback. 9,10,22 Numerous authors strongly endorse a central PFT test oversight with technologist feedback as a vital part of a quality assurance program.…”

A new maximal bicycle test using a prediction algorithm developed from four large COPD studies

“…However, the multicentre data includes many centres with different qualities in performing a correct W MAX test. For DLCO, problems with standardisation across centres and large coefficients of variation have been observed [34]. A good and generalizable prediction algorithm could be helpful to achieve the best possible measured W MAX in order to have the 75% level in the endurance test as accurate as possible.…”

Long-Term Stability of a Portable Carbon Monoxide Single-Breath Diffusing Capacity Instrument

“…Several factors affect the false positive and false negative rates for the interpretation of D LCO results. 12 These include the training and enthusiasm of the technologist performing the tests for meeting guidelines for maneuver acceptability and repeatability 13 ; the accuracy and reproducibility of the instrument 14 ; the inherent biological variability of the patient (including changes in hemoglobin and carboxyhemoglobin); the degree of D LCO impairment (a very low VC or very low D LCO causes low sample volumes, which cause errors in some instruments); the choice of reference equations (especially for very elderly patients and those with non-white ethnicity); thresholds for abnormality (80% predicted vs the 5th percentile lower limit of the normal range); the availability of clinical information that can be used to estimate the pretest probability of various diseases that can affect the D LCO ; and the training, experience, and skill of the physician who interprets the test results (especially those with suboptimal quality). A quality control program for the instrument substantially improves the accuracy and visit-to-visit repro- ducibility of D LCO results [15][16][17] but does not address the other factors, so a comprehensive approach is needed to minimize misclassification and optimize the value of the test for clinical decision making.…”