Accurate diagnosis of idiopathic pulmonary fibrosis (IPF) requires multidisciplinary diagnosis that includes clinical, radiologic, and often pathologic assessment. In 2018, the American Thoracic Society, European Respiratory Society, Japanese Respiratory Society, and the Latin American Thoracic Society (ATS/ERS/JRS/ALAT) and the Fleischner Society each published guidelines for the diagnosis of IPF, which include criteria for 4 categories of confidence of a histologic usual interstitial pneumonia (UIP) pattern.


To (1) identify the role of the guidelines in pathologic assessment of UIP; (2) analyze the 4 guideline categories, including potential areas of difficulty; and (3) determine steps the Pulmonary Pathology Society and the greater pulmonary pathology community can take to improve current guideline criteria and histopathologic diagnosis of interstitial lung disease.

Data Sources.—

Data were derived from the guidelines, published literature, and clinical experience.


Both guidelines provide pathologists with a tool to relay to the clinician the likelihood that a biopsy represents UIP, and serve as an adjunct, not a replacement, for traditional histologic diagnosis. There are multiple challenges with implementing the guidelines, including (1) lack of clarity on the quantity and quality of histologic findings required, (2) lack of recognition that histologic features cannot be assessed independently, and (3) lack of guidance on how pathologists should incorporate clinical and radiographic information. Current criteria for “probable UIP” and “indeterminate for UIP” hinder accurate reflection of the likelihood of IPF. These challenges highlight the need for further morphologic-based investigations in the field of pulmonary pathology.

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Author notes

Dr Smith is a consultant (slide reviews) for Parexel. Dr Hariri is a consultant for Boehringer Ingelheim and Pliant Therapeutics and a grant award recipient of investigator-initiated grant from Boehringer Ingelheim. Dr Larsen is a consultant (slide reviews) at Veracyte, Inc, and Parexel. Dr Tazelar is a consultant at Parexel. Dr Churg has received lecture fees from Boehringer Ingelheim Canada and Hoffman LaRoche Canada. The other authors have no relevant financial interest in the products or companies described in this article.

* Drs Smith and Hariri contributed equally as co–first author in the conception, writing, editing, and review of the manuscript. Drs Churg and Beasley contributed equally as co–senior author in the conception, oversight, editing, and review of the manuscript.