Factors associated with delayed diagnosis of fibrotic interstitial lung disease: a retrospective cohort study.

BACKGROUND: Timely diagnosis and treatment of fibrotic interstitial lung disease (ILD) is crucial to preserve lung function and limit healthcare costs. However, diagnosis is challenging and thus often delayed. Factors associated with delayed diagnosis of fibrotic ILD are poorly understood. This study assessed time to diagnosis among patients with fibrotic ILD and identified factors associated with diagnostic delay. METHODS: This retrospective cohort study used previously developed algorithms to identify patients from a large integrated tertiary-care health system in the US Midwest with evidence of fibrotic ILD in 2011-2019. Adults identified by these algorithms had their ILD diagnosis and symptom onset date confirmed by chart review. Time from symptom onset to diagnosis was dichotomized as ≤ 6 and > 6 months to assign patients to timely and delayed diagnosis cohorts, respectively. Potential predictors of diagnostic delay (demographics, clinical characteristics, ILD-related symptoms and tests, healthcare use, and healthcare costs) were analyzed by stepwise backward logistic regression and by machine learning using gradient boosting, with the latter illustrated using SHAP (SHapley Additive exPlanations) plots. RESULTS: 239 patients met all selection criteria; 138 (57.7%) experienced delayed diagnosis and 101 (42.3%) timely diagnosis. Mean time from symptom onset to diagnosis was 16.8 months for the overall sample, 27.5 months for patients with delayed diagnosis, and 2.2 months for patients with timely diagnosis. Compared to patients with timely diagnosis, greater proportions of those with delayed diagnosis were female (55.8% vs. 40.2%, p = 0.013) and had gastroesophageal reflux disease (GERD) (47.1% vs. 21.6%, p < 0.001) or rheumatic disease (21.0% vs. 10.9%, p = 0.038). In multivariate logistic regression, GERD (odds ratio [OR] 2.64, 95% confidence interval [CI] 1.39-5.04) and number of complaints of cough (OR 1.09, 95% CI 1.02-1.15) and shortness of breath (OR 1.06, 95% CI 1.02-1.09) were associated with increased odds of delayed diagnosis. SHAP plots yielded similar findings. CONCLUSIONS: Delays in diagnosing fibrotic ILD are common and on average postpone clinical identification by about 2 years from symptom onset. Factors associated with delayed diagnosis include GERD and repeated complaints of cough/shortness of breath. Further research should explore how delayed diagnosis affects clinical outcomes.