UIP pattern (all four features) | Probable UIP pattern | Possible UIP pattern (all three features) | Not UIP pattern (any of the features) |
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 | Organising pneumonia#,¶ |
Presence of fibroblast foci | Absence of features against a diagnosis of UIP suggesting an alternate diagnosis | Absence of features against a diagnosis of UIP suggesting an alternate diagnosis | Granulomas¶ |
Absence of features against a diagnosis of UIP suggesting an alternate diagnosis | OR Honeycomb changes only+ | Marked interstitial inflammatory cell infiltrate away from honeycombing | |
Predominant airway-centred changes | |||
Other features suggestive of an alternate diagnosis |
#: can be associated with acute exacerbation of idiopathic pulmonary fibrosis; ¶: an isolated or occasional granuloma and/or a mild component of organising pneumonia pattern may rarely coexist 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 (HRCT) and can be avoided by pre-operative targeting of biopsy sites away from these areas using HRCT. Reproduced from [2] with permission from the publisher.