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©2013 UpToDate ® Print Email ATS/ERS criteria for diagnosis of idiopathic pulmonary fibrosis in absence of surgical lung biopsy Major criteria Exclusion of other known causes of ILD such as certain drug toxicities, environmental exposures, and connective tissue diseases Abnormal pulmonary function studies that include evidence of restriction (reduced VC, often with an increased FEV1/FVC ratio) and impaired gas exchange [increased P(A-a)O 2 , decreased PaO 2 with rest or exercise or decreased DLco] Bibasilar reticular abnormalities with minimal ground glass opacities on HRCT scans Transbronchial lung biopsy or BAL showing no features to support an alternative diagnosis Minor criteria Age >50 years Insidious onset of otherwise unexplained dyspnea or exertion Duration of illness >3 months Bibasilar, inspiratory crackles (dry or "Velcro"-type in quality) In the immunocompetent adult, the presence of all of the major diagnostic criteria as well as at least three of the four minor criteria increases the likelihood of a correct clinical diagnosis of IPF. BAL: bronchoalveolar lavage; DLco: diffusing capacity of the lung for CO; HRCT: high-resolution computerized tomography; ILD: interstitial lung disease; P(A-a)O 2 : alveolar-arterial pressure differences for O 2 ; VC: vital capacity.