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Imaging Features of Systemic Sclerosis-Associated Interstitial Lung Disease
Published on: June 16, 2020
Impact of reference equations on lung function and outcomes in fibrotic interstitial lung disease
Veronica Marcoux1, Prosanta Mondal2, Ayodeji Adegunsoye3
1Department of Medicine, University of Saskatchewan, Saskatoon, SK, Canada.
Background:
The impact of applying different lung function reference equations and interpretation methods in fibrotic interstitial lung disease (ILD) is poorly understood. We aimed to evaluate disease severity classification, trajectories and prognostic significance of percent-predicted and z-scores of forced vital capacity (FVC) and diffusing capacity of the lung for carbon monoxide (D LCO) using the Global Lung Function Initiative (GLI) reference equations in patients with fibrotic ILD, compared to registry-recorded values.
Methods:
Serial lung function measurements of 5026 patients from three prospective registries were used to calculate percent-predicted and z-scores using 2012- and 2023-GLI FVC reference equations and 2017-GLI D LCO reference equations, which were compared with registry-recorded values. Differences for baseline and longitudinal assessments, classification for lung function impairment severity and progression, and association with transplant-free survival and performance of the ILD-Gender-Age-Physiology model with external validation were assessed.
Results:
Baseline FVC and D LCO percent-predicted values were consistently higher using the 2012- and 2023-GLI FVC and 2017-GLI D LCO reference equations compared to registry-recorded values. The agreements for all percent-predicted reference equations were good for lung function severity classification (unweighted κ for FVC 0.69-0.76, D LCO 0.70), but only moderate for the counterpart z-scores (FVC 0.41-0.50, D LCO 0.45). The largest 1-year declines were observed using the 2023-GLI FVC reference equations and the 2017-GLI D LCO reference equations. Lower baseline GLI and registry-recorded FVC and D LCO values were associated with worse transplant-free survival and had similar performance for risk stratification, except for a lack of association of baseline 2023-GLI FVC percent-predicted and z-scores for adjusted analyses in the non-White cohort.
Conclusions:
Use of different lung function reference equations and interpretation methods may impact disease severity classification and longitudinal trajectory in patients with fibrotic ILD, although prognostic significance is similar, except for 2023-GLI FVC in non-White patients.
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