Relative versus absolute change in forced vital capacity in idiopathic pulmonary fibrosis
- Luca Richeldi1,2,
- Christopher J Ryerson3,
- Joyce S Lee2,
- Paul J Wolters2,
- Laura L Koth2,
- Brett Ley2,
- Brett M Elicker4,
- Kirk D Jones5,
- Talmadge E King Jr2,
- Jay H Ryu6,
- Harold R Collard2
- 1Center for Rare Lung Diseases, University of Modena and Reggio Emilia, Modena, Italy
- 2Department of Medicine, University of California, San Francisco, California, USA
- 3Department of Medicine, University of British Columbia, Vancouver, Canada
- 4Department of Radiology, University of California, San Francisco, California, USA
- 5Department of Pathology, University of California, San Francisco, California, USA
- 6Department of Pulmonary and Critical Care Medicine, Mayo Clinic, Rochester, Minnesota, USA
- Correspondence to Dr Luca Richeldi, Center for Rare Lung Diseases, University of Modena and Reggio Emilia, Policlinico Hospital, Via del Pozzo 71, 41100 Modena, Italy;
Contributors Conception and design: LR, CJR, HRC; analysis and interpretation: LR, CJR, JSL, PJW, LLK, TEK, HRC; drafting the manuscript for important intellectual content: LR, CJR, JSL, PJW, LLK, BL, BME, KDJ, TEK, JHR, HRC.
- Received 1 October 2011
- Accepted 1 March 2012
- Published Online First 17 March 2012
Background Decline in forced vital capacity (FVC) over time reliably predicts mortality in patients with idiopathic pulmonary fibrosis. The use of this measure in clinical practice is recommended by current evidence-based guidelines. It is unknown if the method of calculating decline in FVC (relative vs absolute change) impacts its frequency or its ability to predict mortality.
Methods Patients with idiopathic pulmonary fibrosis from two prospective cohorts were included if they had a baseline and 12-month follow-up FVC. A ≥10% decline in FVC from baseline was calculated in two ways: a relative decline of 10% (eg, from 60% predicted to 54% predicted) and an absolute decline of 10% (eg, from 60% predicted to 50% predicted). The frequency of a ≥10% decline in FVC and its ability to predict 2-year transplant-free survival were compared between these two methods. Declines in FVC of ≥5% and ≥15% were similarly compared. Analyses were performed unadjusted and adjusted for age, gender, use of oxygen, baseline FVC and baseline diffusion capacity for carbon monoxide.
Results The frequency of any given FVC decline was significantly greater using the relative change in FVC method. For ≥10% decline, both methods predicted 2-year transplant-free survival with similar accuracy, and remained significant predictors after adjusting for baseline characteristics. The absolute change method appeared more predictive for ≥5% decline.
Conclusions Using the relative change in FVC maximises the chance of identifying a ≥10% decline in FVC without sacrificing prognostic accuracy. This may not hold true for ≥5% decline in FVC. These findings have important implications for clinical practice and the design of clinical trials.
- Interstitial fibrosis
- rare lung diseases
- respiratory infection
- alveolar proteinosis
- pulmonary rehabilitation
- clinical epidemiology
- systemic disease and lungs
LR and CJR contributed equally to this manuscript.
Funding NIH grant HL086516 (HRC).
Correction notice This article has been corrected since it was published online first. The author names now read Brett Ley and Brett M Elicker. The following sentence has been updated to read: ‘The mean age at the time of diagnosis was 67 years, most patients were men with a history of smoking, and more than half had surgical lung biopsy.’
Competing interests None to declare.
Patient consent Obtained.
Ethics approval Ethics committee of UCSF and Mayo Clinic.
Provenance and peer review Not commissioned; externally peer reviewed.