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Cystic Fibrosis Disease–specific Centiles in 2000 and 2005

We thank Stanke and colleagues for their comments on our recent article (1), and for turning our attention to the existence of centile equations for FEV₁% predicted among patients with cystic fibrosis (CF) (2). We agree that our statement was not correct and that we should have stated, "we have published the first disease-specific lung function reference equations." Unfortunately, the percentile equations (FEVPerc) referred to by Stanke and colleagues and the methodology used to develop them remain unpublished. Stanke and coworkers demonstrate that the FEVPerc percentiles have been successfully applied in several research papers. However, publication of the percentile equations and public availability of the software are necessary to make this technique accessible to the whole CF research community.

The fundamental difference between our percentiles and FEVPerc is that we developed CF-specific percentiles for raw FEV₁ in liters while FEVPerc provides an age-dependent CF-specific reference for FEV₁% predicted. With our approach, one can choose whether the percentiles are standardized for height alone, age alone, or both height and age. FEVPerc does not standardize for height within the CF population; it is based on height standardization developed for a healthy population. The impaired growth of patients with CF affects FEVPerc percentiles but not our percentiles.

Michal Kulich

Charles University, Prague, Czech Republic

Margaret Rosenfeld and Bonnie Ramsey

University of Washington, Seattle, Washington

FOOTNOTES

Conflict of Interest Statement: None of the authors have a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Kulich M, Rosenfeld M, Campbell J, Kronmal R, Gibson RL, Goss CH, Ramsey B. Disease-specific reference equations for lung function in patients with cystic fibrosis. Am J Respir Crit Care Med 2005;172:885–891.[Abstract/Free Full Text]
2. Mekus F, Ballmann M, Bronsveld I, Bijman J, Veeze H, Tümmler B. Categories of deltaF508 homozygous cystic fibrosis twin and sibling pairs with distinct phenotypic characteristics. Twin Res 2000;3:277–293.[CrossRef][Medline]

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