| 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 PA–aO2, decreased PaO2 with rest or exercise, or decreased DLCO) |
| Bibasilar reticular abnormalities with minimal ground-glass opacities on HRCT |
| Transbronchial lung biopsy or BAL showing no features to support an alternative diagnosis |
| Minor criteria |
| Age >50 years |
| Insidious onset of otherwise unexplained dyspnoea on 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 idiopathic pulmonary fibrosis. See figure 2 for the updated 2011 criteria. ILD: interstitial lung disease; VC: vital capacity; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; PA–aO2: alveolar–arterial oxygen tension difference; PaO2: arterial oxygen tension; DLCO: diffusing capacity of the lung for carbon monoxide; HRCT: high-resolution computed tomography; BAL: bronchoalveolar lavage. Data from [10].