Peripheral and alveolar biomarkers of fibrotic hypersensitivity pneumonitis

Fibrotic hypersensitivity pneumonitis (fHP) is a frequently misdiagnosed fibrosing interstitial pneumonia, which often remains undiagnosed due to the lack of uniformity of diagnostic criteria. Its features are similar to those of other ILDs, especially idiopathic pulmonary fibrosis (IPF), and biomarkers with potential clinical value have been proposed. We reviewed the recent literature on serum and BAL biomarkers, focusing on their clinical role in the diagnosis and management of fHP. We searched Medline/Pubmed results from 2005 until April 2020. The manuscripts of interest selected by our search were limited in number and proposed different clinical biomarkers in serum (IgG antibodies, macrophage inflam-matory proteins-1, epithelial cell proteins) and BAL (lymphocytes, T-cell mediators). This is the first review to summarize all the serum and BAL biomarkers for fHP proposed in the literature. This review summarized the main biomarkers investigated in fibrotic hypersensitivity pneumonitis because an urgent aim of subsequent research will be to validate and standardize them for diagnostic purposes.