Relative versus absolute change in forced vital capacity in idiopathic pulmonary fibrosis.

TitleRelative versus absolute change in forced vital capacity in idiopathic pulmonary fibrosis.
Publication TypeJournal Article
Year of Publication2012
AuthorsRicheldi, L, Ryerson, CJ, Lee, JS, Wolters, PJ, Koth, LL, Ley, B, Elicker, BM, Jones, KD, King, TE, Ryu, JH, Collard, HR
JournalThorax
Volume67
Issue5
Pagination407-11
Date Published2012 May
ISSN1468-3296
KeywordsFemale, Follow-Up Studies, Humans, Idiopathic Pulmonary Fibrosis, Logistic Models, Lung Transplantation, Male, Survival Analysis, Vital Capacity
Abstract

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% (e.g., from 60% predicted to 54% predicted) and an absolute decline of 10% (e.g., 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.

DOI10.1136/thoraxjnl-2011-201184
Alternate JournalThorax
PubMed ID22426899
Grant ListHL086516 / HL / NHLBI NIH HHS / United States