BACKGROUND: Hypersensitivity pneumonitis (HP) is a diffuse parenchymal lung disease characterized by immune-mediated inflammation of lung parenchyma triggered by exposure to a wide variety of inhaled antigens. YKL-40 plays a fundamental role in protecting against pathogens, antigen-induced and oxidant-induced injury responses, inflammation, and tissue repair and remodeling. This is achieved by regulating many biological processes.OBJECTIVE: The aim of this study was to evaluate the YKL-40 serum level as a possible biomarker for disease activity in hypersensitivity pneumonitis.




METHODS: The study included 25 patients who were diagnosed primarily as hypersensitivity pneumonitis in Chest Department, Faculty of Medicine, Cairo University from April 2021 to August 2021. Moreover, 25 healthy age- and sex-matched controls were enrolled.RESULTS: YKL-40 was significantly higher among HP group, in fibrotic more that non-fibrotic subtype. YKL-40 had a negative correlation with oxygen saturation (SaO2) on room air, minimum SO2 in 6MWT and distance in 6MWT in HP patients. In addition, YKL-40 has a positive correlation with dyspnea score in HP patients. The fibrotic subgroup, compared to non-fibrotic subgroup had significantly higher serum YKL-40 level. A cut-off value of 629.4 pg/ml for serum YKL-40 level can distinguish between the HP patients and normal individuals (sensitivity =96%, and specificity =96%). Moreover, a cut-off value of 1181.5 pg/ml for serum YKL-40 level can distinguish between the fibrotic and non-fibrotic HP sub-types (sensitivity =85.7%, and specificity =81.8%).CONCLUSION: YKL-40 is a useful prognostic marker for hypersensitivity pneumonitis and can help in discriminating between fibrotic and non-fibrotic subtypes.