Rationale: Interstitial lung abnormalities (ILAs) are being increasingly identified in clinical practice. In particular, for subpleural nonfibrotic ILAs, the risk of progression over time and the risk factors for progressive behavior are still largely unknown. Objectives: To determine the age band prevalence of ILAs and the risk of radiological progression of subpleural nonfibrotic ILAs over time in a large health checkup population and to identify how reticulation contributes to the risk of radiological progression. Methods: On the basis of the ILAs definition by the Fleischner Society, low-dose chest computed tomography images from the community-dwelling population who have undergone health checkups were evaluated for ILAs. Multivariable logistic regression was used to assess the risk of radiological progression. Measurements and Main Results: Among 155,539 individuals, 3,300 (2.1%) were confirmed to have ILAs: the vast majority (81.7%) were defined as subpleural nonfibrotic ILAs. The prevalence of ILAs increased linearly with age (P for trend < 0.0001). Of 454 individuals with subpleural nonfibrotic ILAs, 198 (43.6%) had radiological progression over 4 years. The presence of reticulation on initial imaging was an independent predictor of radiological progression (odds ratio, 1.9; 95% confidence interval, 1.2-3.0; P = 0.0040). No difference in radiological progression was identified between subpleural nonfibrotic ILAs with extensive reticulation and subpleural fibrotic ILAs (73.0% vs. 68.8%; P = 0.7626). Conclusions: The prevalence of ILAs increases linearly with age. Nearly half of subpleural nonfibrotic ILAs progress radiologically over 4 years. The presence of reticulation is a risk factor for radiological progression. Subpleural nonfibrotic ILAs with extensive reticulation are likely to be a feature of subpleural fibrotic ILAs.

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