Marginal decline in forced vital capacity is associated with a poor outcome in idiopathic pulmonary fibrosis

In therapeutic studies in idiopathic pulmonary fibrosis (IPF), the low prevalence of significant change in pulmonary functional tests (PFTs) has been a major constraint. The prognostic value of marginal'' changes in PFTs in IPF and fibrotic non-specific interstitial pneumonia (NSIP) was evaluated. In patients with biopsy-proven IPF (n=84) and NSIP (n=72), forced vital capacity (FVC) and diffusing capacity of the lung for carbon monoxide (DL,CO) trends at 6 months were categorised as significant'' (FVC >10%; DL,CO >15%) or marginal'' (FVC 5-10%; DL,CO 7.5-15%). Proportional hazards analysis and time-dependent receiver operating characteristic methodology were used to examine PFT trends against mortality. In IPF, reductions in FVC were significant in 22 cases (26%) and marginal in 19 cases (23%). Mortality was higher in patients with a significant decline in FVC (hazard ratio (HR) 2.80, 95% CI 1.54-5.06; p<0.001) and those with a marginal decline in FVC (HR 2.31, 95% CI 1.19-4.50; p=0.01) than in those with stable disease. Progression-free survival was lower when the decline in FVC was marginal than in stable disease (HR 2.34, 95% CI 1.19-4.60; p=0.01). Marginal changes in DL,CO in IPF and marginal changes in FVC and DL,CO in fibrotic NSIP did not provide useful prognostic information. Marginal change in FVC in IPF denotes a poor outcome. These findings are applicable to clinical practice and to the selection of patients with more progressive disease for therapeutic studies.