In contrast, circulating GDF15 has been introduced as a prognostic protein, and elevated concentrations of circulating GDF15 have been observed in atherosclerotic, ischaemic, and cardiac fibrotic conditions [7]; higher circulating GDF15 levels were found in patients with fibrotic hypersensitivity pneumonitis than in those with non-fibrotic hypersensitivity pneumonitis [8]. This evidence concerns the gene GDF15 and hypersensitivity pneumonitis.