Published ahead of print on June 23, 2005, doi:10.1164/rccm.200410-1335OC Am. J. Respir. Crit. Care Med., Volume 172, Number 7, October 2005, 885-891 A more recent version of this article appeared on October 1, 2005
Submitted on October 8, 2004 Disease-Specific Reference Equations for Lung Function in Patients with Cystic FibrosisMichal Kulich1*,1 Department of Probability and Statistics, Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic, 2 Division of Pulmonary Medicine, Department of Pediatrics, University of Washington, Seattle, WA, USA, 3 Department of Pharmacy, University of Washington, Seattle, WA, USA, 4 Department of Biostatistics, University of Washington, Seattle, WA, USA, 5 Cystic Fibrosis Therapeutic Development Network Coordinating Center, Children's Hospital and Regional Medical Center, Seattle, WA, USA; Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Washington, Seattle, WA, USA, 6 Division of Pulmonary Medicine, Department of Pediatrics, University of Washington, Seattle, WA, USA; Cystic Fibrosis Therapeutic Development Network Coordinating Center, Children's Hospital and Regional Medical Center, Seattle, WA, USA * To whom correspondence should be addressed. E-mail: kulich{at}karlin.mff.cuni.cz.
Rationale: Forced expiratory volume in one second (FEV1), an important measure of pulmonary disease severity in cystic fibrosis (CF) patients, is frequently expressed as a percentage of a predicted value derived from a healthy reference population. There are limitations to comparing the lung function of a CF patient to that of healthy controls, and potential advantages to comparing it to that of other CF patients. Objective: To estimate CF-specific percentiles of FEV1 as functions of height, age, and gender. Methods: We used 287,108 FEV1 observations among >21,000 CF patients in the CF Foundation National Patient Registry between 1994 and 2001. The percentiles were estimated using quantile regression methods. Results: FEV1 percentile "growth grids" are presented allowing comparison of an individual's FEV1 to that of CF patients of the same gender, age and height. Their potential uses in clinical practice and research are illustrated. Conclusions: CF-specific reference equations allow individual patients' FEV1 to be placed in the context of the distribution of lung function of their peers with CF, and should improve generalizability of CF clinical trials by setting entry criteria that are equitable across gender and age ranges. They may serve as a useful adjunct to conventional reference equations. Key words: cystic fibrosis, lung function, percentile, reference equations
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