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Thorax. 2012 May;67(5):407-11. doi: 10.1136/thoraxjnl-2011-201184. Epub 2012 Mar 17.

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

Author information

1
Center for Rare Lung Diseases, University of Modena and Reggio Emilia, Policlinico Hospital, Via del Pozzo 71, 41100 Modena, Italy. luca.richeldi@unimore.it

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.

PMID:
22426899
DOI:
10.1136/thoraxjnl-2011-201184
[Indexed for MEDLINE]

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