Guideline on the Diagnosis of Hypersensitivity Pneumonitis Is Released

The American Thoracic Society, the Japanese Respiratory Society, and the Asociación Latinoamericana del Tórax have developed a clinical practice guideline for the diagnosis of hypersensitivity pneumonitis (HP).

“The main objective is to help clinicians who are evaluating patients with newly identified [interstitial lung disease] ILD to accurately recognize nonfibrotic HP and fibrotic HP in a timely manner that will lead to avoidance of culprit environmental factors and potentially change the disease course,” the guideline authors wrote.

To develop guidance for a systematic approach to the diagnosis of HP, the multidisciplinary panel performed systematic reviews of available literature. Based off this evidence, the panel wrote that clinicians must consider HP in the differential diagnosis for patients with newly identified ILD.

The guideline committee categorized HP into two clinical phenotypes—nonfibrotic HP and fibrotic HP—and made recommendations (strong recommendations) and suggestions (weak or conditional recommendations) for each.

The panel recommended that bronchoalveolar lavage (BAL) fluid be obtained for lymphocyte cellular analysis among patients with clinical and radiographic manifestations suggestive of nonfibrotic HP. It was also suggested that, among this patient population, the following be performed:

  • Serum IgG testing that targets potential antigens associated with HP 
  • Transbronchial forceps lung biopsy
  • Surgical lung biopsy only when all other diagnostic testing has not yielded a diagnosis 


For patients with clinical and radiographic manifestations suggestive of fibrotic HP, the panel made the following suggestions:

  • Perform serum IgG testing that targets potential antigens associated with HP
  • Obtain BAL fluid for lymphocyte cellular analysis
  • Perform transbronchial lung cryobiopsy
  • Perform surgical lung biopsy when all other diagnostic testing has not yielded a diagnosis 


While the panel did not make a recommendation or suggestion for or against the use of a questionnaire to identify potential HP-inciting agents and sources, it did recommend that a questionnaire be developed and validated. 

In addition to this diagnostic guidance, the authors defined HP and included sections on the clinical manifestations, pathogenesis, radiological features, histopathological features, and diagnostic criteria. 

The panel also identified knowledge gaps in the understanding of the nature and pathophysiology of HP, as well as in diagnostic approaches, disease behavior and natural history, and therapeutic approaches.

“Now that this guideline has established a standardized diagnostic approach to HP, future work needs to address the management of the different subtypes of HP in clinical trials and other research,” the authors wrote.

—Colleen Murphy


Raghu G, Remy-Jardin M, Ryerson CJ, et al. Diagnosis of hypersensitivity pneumonitis in adults. An official ATS/JRS/ALAT clinical practice guideline. Am J Respir Crit Care Med. 2020;202(3):e36-e69. doi:10.1164/rccm.202005-2032ST