Table 2.

Histopathological Criteria for the UIP Pattern.

UIP	Probable UIP	Indeterminate for UIP	Alternative diagnosis
- Evidence of marked fibrosis / architectural distortion, ± honeycombing in a predominantly subpleural / paraseptal distribution - Patchy involvement of lung parenchyma by fibrosis - Fibroblast foci	- Some characteristics of column 1 but not sufficient to corroborate the diagnosis of UIP- Exclusively honeycombing changes - Absence of features to suggest an alternative diagnosis	- Some histologic features of column 1 associated with features that suggest another diagnosis or UIP secondary to another cause (granulomas, hyaline membranes, cellular inflammatory infiltrate in areas away from honeycombing, prominent lymphoid hyperplasia, bronchiolocentric distribution, exuberant chronic fibrous pleuritis and organizing pneumonia)	- Hyaline membranes - Organizing pneumonia - Granulomas - Marked interstitial inflammatory cell infiltrate away from honeycombing - Predominant airway-centered changes - Other features suggestive of an alternate diagnosis

UIP: Usual Interstitial Pneumonia.

Adapted from Raghu et al. (6).