Specific diagnostic HRCT criteria for usual interstitial pneumonia (UIP) pattern have been proposedadopted by international consensus of ATS/ERS/JRS/ALAT to categorise CT-based certainty for the UP pattern into three levels: definite UIP, probable UIP and inconsistent with UIP.

This helps radiologists to determine the certainty of UIP diagnosis based on HRCT chest findings. The importance of this guideline is that definite UIP pattern on chest HRCT precludes the need for tissue diagnosis ^1,2. However unfortunately up to 20 % of inconsistent with UIP group (or actually atypical UIP) can be UIP on biopsy or IPF in clinical course.

UIP pattern

• All four features present:
  • subpleural, basal predominance
  • reticular abnormality
  • honeycombing +/- traction bronchiectasis
  • absence of features listed as "inconsistent with UIP" (see below)

Possible UIP pattern

• All three features present^*:
  • subpleural, basal predominance
  • reticular abnormality
  • absence of features listed as "inconsistent with UIP" (see below)

               ^{* honeycombing is absent}

Inconsistent with UIP pattern

• Any one of the following seven features present:
  • upper or mid-lung predominance
  • peribronchovascular predominance
  • extensive ground glass abnormality (i.e. more than reticular abnormality)
  • profuse micronodules (bilateral, predominantly upper lobes)
  • discrete cysts (multiple, bilateral, away from honeycombing)
  • diffuse mosaic attenuation / air-trapping (bilateral in ≥3 lobes)
  • consolidation in bronchopulmonary segment(s) or lobe(s)

See also:

ATS criteria for diagnosis of UIP on pathology