Healthcare utilisation preceding the diagnosis of interstitial lung disease.

Background: Diagnosis of interstitial lung disease (ILD) is frequently delayed, as symptoms are misattributed to other lung or cardiac diseases. Identifying prediagnostic patterns in healthcare utilisation may highlight areas of intervention leading to earlier diagnosis and treatment, potentially improving prognosis. We aimed to investigate healthcare utilisation in primary and secondary care in ILD patients compared to matched references over 10 years preceding the ILD diagnosis, using nationwide Danish registers and adjusting for comorbidities. Methods: We conducted a nationwide matched cohort study using data from national registers. The study population was patients with a first-time diagnosis of ILD between 1 January 2011 and 31 December 2019. Cases were matched with 10 references. Outcomes included number of hospital contacts, chest radiographs or computed tomography, and general practitioner consultations, spirometries, and C-reactive protein measurements. Incidence rate ratios (IRRs) were calculated using multivariate negative binomial regression models, adjusted for socioeconomic factors and comorbidities. Results: We identified 13 161 cases with ILD, matched with 131 620 references. Mean±sd age at diagnosis was 68.4±13.9 years, with a slight male predominance. Most adjusted IRRs were elevated for up to 10 years preceding diagnosis, steadily increasing and sharply peaking 1 year prior to diagnosis. Similar patterns were seen when stratifying analyses for comorbidities. The adjusted IRRs were generally higher for patients without comorbidities. Conclusions: This nationwide study shows an increase in healthcare utilisation in both primary and secondary care in ILD patients up to 10 years before diagnosis, indicating a diagnostic delay longer than previously reported.