Table 2. Histopathological criteria for a diagnosis of UIP.

Findings	UIP pattern	Probable UIP	Possible UIP
Marked fibrosis, architectural distortion ± honeycombing in a predominantly subpleural distribution	✓	–	–
Marked fibrosis, architectural distortion ± honeycombing*	–	✓	–
Patchy or diffuse lung fibrosis ± interstitial inflammation	–	–	✓
Patchy areas of fibrosis and fibroblastic foci	✓	–	–
Patchy areas of fibrosis or fibroblastic foci	–	✓	–
Absence of features against the diagnosis of UIP (see text)	✓	✓	✓

*, probable UIP may also be considered with only honeycomb changes. UIP, usual interstitial pneumonia.