MUC1 and idiopathic pulmonary fibrosis: As expected, there were several differences between the patients with IPF and iPPFE; there were more male smokers and levels of serum Krebs von den Lungen-6 (KL-6) were increased in the IPF group, whilst patients with iPPFE had lower BMIs (median 17.2 [14.7–18.5] kg/m2), occasional “flattened chest” as previously described18,20,21, lower % forced vital capacity (FVC)-predicted, and higher partial pressures of carbon dioxide (PaCO2).