Fig. 1

Diagnostic algorithm for fibrotic HP with patients stratified by presence (red) or absence (blue) of an identified antigen exposure. *Radiological HP pattern: Combination of mosaic attenuation, ground-glass and normal lung, or a combination of mosaic attenuation and signs of fibrosis. ^†Radiological definite and probable usual interstitial pneumonia (UIP) based on the 2018 diagnostic criteria for IPF. ^‡Pathological HP pattern: Chronic bronchiolocentric inflammation, poorly formed non-necrotizing granulomas, giant cells, airway-centred interstitial fibrosis, absence of an alternative diagnosis. BAL bronchoalveolar lavage, HP hypersensitivity pneumonitis, IPF idiopathic pulmonary fibrosis; UIP usual interstitial pneumonia