The impact of a new reference value set for diffusing capacity for patients with idiopathic pulmonary fibrosis.

Abstract

Background: Idiopathic pulmonary fibrosis (IPF) is a progressive life threatening lung disease for which no cure exists. IPF patients are often eager to participate in clinical trials. The Global Lung Function Initiative (GLI) recently reported new reference values for the carbon monoxide transfer factor of the lung (TLCO). Most clinical trials in IPF use lung function inclusion criteria. This study aims to assess the impact of the new TLCO reference values on trial inclusion in IPF. Methods: We used complete and correct lung function data of IPF patients routinely collected in 2017. TLCO%pred was calculated using European Community for Steel and Coal reference values 1993 (ECSC) and the new GLI (2017) reference values. We compared the number of patients eligible for clinical trials that use TLCO≥30%pred as inclusion criteria. Results: We included data of 145 patients (118 men), mean age 72 years (±8). Mean FVC was 75%pred (±16) using GLI. Calculated with ECSC equations and GLI equations, the median (interquartile range) TLCO, transfer coefficient KCO and alveolar volume VA were respectively 35%pred (28-44) vs 37%pred (29-46), 66%pred (55-78) vs 64%pred (52-73) and 55%pred (48-64) vs 60%pred (53-69). With an inclusion threshold set at TLCO≥30%pred, 96 patients (66%) would fall into the eligible range using ECSC, and 104 patients (72%) when using GLI. These 8 patients were close to the 30% threshold, with a TLCO of 28%- 29%pred using ECSC. Conclusion: Switching to the new GLI 2017 reference values for TLCO may have small positive effect on trial inclusion for the individual patient with IPF. Physicians should be aware of this impact when choosing reference values.