Major criteria:
(1) exclusion of other known causes of interstitial lung disease (drug toxicity, environmental exposures, connective tissue disease)
(2) abnormal findings on pulmonary function studies, including:
(2a) evidence of restriction (reduced vital capacity, often with an increase in the FEV1 to FVC ratio)
(2b) impaired gas exchange (increased alveolar-arterial oxygen gradient with rest or exercise, or a decreased diffusion capacity for carbon monoxide)
(3) bibasilar reticular abnormalities with minimal ground glass opacities on high-resolution computed tomography (HRCT)
(4) transbronchial lung biopsy or bronchoalveolar lavage (BAL) showing no features to support an alternative diagnosis
Minor criteria:
(1) age > 50 years
(2) insidious onset of unexplained dyspnea on exertion
(3) duration of illness for 3 or more months
(4) bibasilar inspiratory dry crackles ("Velcro type")
The clinical diagnosis of idiopathic pulmonary fibrosis:
(1) all 4 major criteria, AND
(2) >= 3 minor criteria
