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Standardization of the Single-Breath Diffusing Capacity in a Multicenter Clinical Trial^*

^* From the Johns Hopkins University School of Medicine (Dr. Wise), Baltimore, MD; Pfizer Global Research and Development (Drs. Teeter, England, Schwartz, and Riese), New London, CT; LDS Hospital and University of Utah (Drs. Jensen and Crapo), Salt Lake City, UT; Ferraris Respiratory (Mr. Giles), Louisville, CO; University of Iowa Carver College of Medicine (Dr. Ahrens), Iowa City, IA; and Duke University Medical Center (Dr. MacIntyre), Durham, NC.

Correspondence to: Robert A. Wise, MD, FCCP, Johns Hopkins Asthma & Allergy Center, 5501 Hopkins Bayview Circle, Baltimore, MD 21224; e-mail: rwise{at}jhmi.edu

Abstract

Background: Standardization of the measurement of single-breath diffusing capacity of the lung for carbon monoxide (DLCO) is difficult to implement in multicenter trials as differences in equipment, training, and performance guidelines have led to high variability between and within centers. The safety assessment of inhalable insulin required the standardization of measurement of single-breath DLCO in multicenter clinical trials to optimize test precision.

Methods: This was an open-label, 24-week, parallel-group, outpatient study of inhaled human insulin in participants with type 1 diabetes who were randomly assigned to receive treatment with daily premeal inhaled or subcutaneous (SC) insulin for 12 weeks, followed by SC insulin for 12 weeks. Monitoring of single-breath DLCO using standardized methodology was performed. Standardization included uniform instrumentation, centrally trained study coordinators, and centralized data monitoring and review of quality control. Sites received feedback within 24 h for any tests of unacceptable quality with recommendations for improvement.

Results: A total of 226 study participants at 33 sites completed 11,335 DLCO efforts during 4,797 test sessions; 3,607 (75.2%) and 4,581 (95.5%) of all testing sessions yielded two American Thoracic Society-acceptable efforts that varied by < 1 and 2 mL/min/mm Hg, respectively. Only 65 sessions produced one or fewer acceptable efforts. The root mean square intrasubject coefficient of variation in DLCO at the end of the comparative dosing phase was 6.01%.

Conclusions: The standardized methodology employed in this study demonstrates the feasibility of collecting high-quality single-breath DLCO data in the setting of a multicenter clinical trial with reliability that is comparable to spirometry.

Key Words: clinical trials • diffusing capacity • inhaled human insulin • methodology • respiratory function tests