MUC1 and hypersensitivity pneumonitis: Ohnishi et al. reported that the serum concentrations of KL-6 in four patients with DRP-HP were all within normal limits (cutoff level: 520 U/mL), as well as eosinophilic pneumonia and organizing pneumonia patterns, at the time of their diagnosis, even in patients with a large extent of opacities [14].