Diagnosis of Hypersensitivity Pneumonitis in Adults: An Official ATS/JRS/ALAT Clinical Practice Guideline.

BACKGROUND This guideline addresses the diagnosis of hypersensitivity pneumonitis (HP). It represents a collaborative effort between the American Thoracic Society, Japanese Respiratory Society, and Asociacion Latinoamericana de Torax. METHODS Systematic reviews were performed for six questions. The evidence was discussed and then recommendations formulated by a multidisciplinary committee of experts in the field of interstitial lung disease and hypersensitivity pneumonitis (HP) using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. RESULTS The guideline committee defined HP and clinical, radiographic, and pathologic features were described. HP was classified into non-fibrotic and fibrotic phenotypes. There was limited evidence that was directly applicable to all questions. The need for a thorough history and a validated questionnaire to identify potential exposures was agreed upon. Serum IgG testing against potential antigens associated with HP was suggested to identify potential exposures. For patients with non-fibrotic HP, a recommendation was made in favor of obtaining bronchoalveolar lavage fluid for lymphocyte cellular analysis, as well as suggestions for transbronchial lung biopsy and surgical lung biopsy. For patients with fibrotic HP, suggestions were made in favor of obtaining bronchoalveolar lavage fluid for lymphocyte cellular analysis, transbronchial lung cryobiopsy, and surgical lung biopsy. Diagnostic criteria were established and a diagnostic algorithm was created by expert consensus. Knowledge gaps were identified as future research directions. CONCLUSIONS The guideline committee developed a systematic approach to the diagnosis of HP. The approach should be reevaluated as new evidence accumulates.