Table 2. High-Resolution CT Criteria for UIP Pattern Proposed by ATS/ERS/JRS/ALAT in 2018.

UIP	Probable UIP	Indeterminate UIP	Alternative Diagnosis
• Subpleural and basal predominant; distribution is often heterogeneous	• Subpleural and basal predominant; distribution is often heterogeneous	• Subpleural and basal predominant	Findings suggestive of another diagnosis, including: • CT features:  - Cysts  - Marked mosaic attenuation  - Predominant GGO  - Profuse micronodules  - Centrilobular nodules  - Nodules  - Consolidation • Predominant distribution:  - Peribronchovascular  - Perilymphatic  - Upper or mid-lung • Other:  - Pleural plaques (consider asbestosis)  - Dilated esophagus (consider CTD)  - Distal clavicular erosions (consider RA)  - Extensive lymph node enlargement (consider other etiologies)  - Pleural effusions, pleural thickening (consider CTD/drugs)
• Honeycombing with or without peripheral traction bronchiectasis or bronchiolectasis	• Reticular pattern with peripheral traction bronchiectasis or bronchiolectasis	• Subtle reticulation; may have mild GGO or distortion (“early UIP pattern”)
	• May have mild GGO	• CT features and/or distribution of lung fibrosis that do not suggest any specific etiology (“truly indeterminate for UIP”)

Adapted from Raghu et al. Am J Respir Crit Care Med 2018;198:e44-e68 (7).

ATS/ERS/JRS/ALAT = American Thoracic Society/European Respiratory Society/Japanese Respiratory Society/Latin American Thoracic Society, CTD = connective tissue disease, GGO = ground-glass opacity, RA = rheumatoid arthritis, UIP = usual interstitial pneumonia