KL-6 levels were higher in idiopathic pulmonary fibrosis (IPF) than fibrotic hypersensitivity pneumonitis (fHP) (105.6 ng/mL vs. 65.87 ng/mL; p=0.0409), in patients who died (109.8 ng/mL vs. 68.6 ng/mL; p=0.022), and in the MUC5B (rs35705950) GT/TT genotype (85.07 ng/mL vs. 65.58 ng/mL; p=0.019). This evidence concerns the gene MUC5B and hypersensitivity pneumonitis.