The American Thoracic Society (ATS) has provided criteria for making the clinical diagnosis of idiopathic pulmonary fibrosis.
(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
(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
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