| UIP pattern# | Probable UIP pattern | Possible UIP pattern¶ | Not UIP pattern+ |
| Evidence of marked fibrosis/architectural distortion±honeycombing in a predominantly subpleural/paraseptal distribution | Evidence of marked fibrosis/architectural distortion±honeycombing | Patchy or diffuse involvement of lung parenchyma by fibrosis, with or without interstitial inflammation | Hyaline membranes§ |
| Presence of patchy involvement of lung parenchyma by fibrosis | Absence of either patchy involvement or fibroblastic foci, but not both | Absence of other criteria for UIP (see first column) | Organising pneumonia§,ƒ |
| Presence of fibroblast foci | Absence of features against a diagnosis of UIP suggesting an alternative diagnosis (see fourth column) OR Honeycomb changes only## | Absence of features against a diagnosis of UIP suggesting an alternative diagnosis (see fourth column) | Granulomasƒ |
| Absence of features against a diagnosis of UIP suggesting an alternative diagnosis (see fourth column) | Marked interstitial inflammatory cell infiltrate away from honeycombing | ||
| Predominant airway centred changes | |||
| Other features suggestive of an alternative diagnosis |
#: all four features. ¶: all three features. +: any of the six features. §: can be associated with acute exacerbation of idiopathic pulmonary fibrosis. ƒ: an isolated or occasional granuloma and/or a mild component of organising pneumonia pattern may rarely be co-existing in lung biopsies with an otherwise UIP pattern. ##: this scenario usually represents end-stage fibrotic lung disease where honeycombed segments have been sampled but where a UIP pattern might be present in other areas. Such areas are usually represented by overt honeycombing on high-resolution computed tomography and can be avoided by pre-operative targeting of biopsy sites away from these areas using high-resolution computed tomography. Reproduced from [2] with permission from the publisher.