Evaluation of subclinical pulmonary involvement in inflammatory bowel disease using spirometry: an observational study

Background Crohn’s disease and ulcerative colitis are the two main forms of inflammatory bowel disease (IBD), a chronic relapsing inflammatory disorder that may be associated with extraintestinal manifestations, including subclinical pulmonary involvement. Because the gastrointestinal and respiratory tracts share embryological and immunological characteristics, pulmonary abnormalities may occur even in the absence of respiratory symptoms. Spirometry is a simple, non-invasive, and widely available tool that may facilitate the early detection of these subclinical pulmonary changes. Objective To evaluate the presence of subclinical pulmonary dysfunction in patients with IBD using spirometry and to correlate pulmonary function parameters with disease activity. Methods A prospective observational cohort study included 80 IBD patients (41 in remission, 39 active phases) recruited from IBD clinic of Tropical Medicine and Gastroenterology Department at Alrajhi Hospital, Assiut University and 20 healthy controls, with no known respiratory diseases. All participants underwent detailed clinical assessment, laboratory investigations and spirometric evaluation, including FEV₁, FVC, FEV₁/FVC ratio, and small airway parameters (FEF25–75%, MEF25, MEF50, MEF75). IBD activity was assessed using endoscopy, Magnetic Resonance Enterography (MRE) +_ intestinal ultrasound (IUS) for CD and endoscopic Mayo score for UC. Correlation analyses were performed to evaluate the diagnostic utility of spirometric indices and their relationship to IBD activity. Results A significant proportion of IBD patients showed abnormal spirometric findings despite being asymptomatic. Small airway indices (e.g., FEF25–75%, MEF50) demonastrate Difference between IBD pts and healthy control to traditional spirometric measures. Disease activity markers, particularly fecal calprotectin, showed weak-to-moderate correlations with selected pulmonary function parameters. No significant differences were found between active and inactive IBD in conventional parameters, but subtle changes were captured in small airway indices. Conclusions Subclinical pulmonary dysfunction is prevalent among IBD patients, with small airway involvement being a key feature. Spirometry, particularly small airway indices, may serve as a useful, non-invasive screening tool for detection of early pulmonary impairment in this population. Routine pulmonary function monitoring should be considered, even in asymptomatic IBD patients. Clinical trial number gov NCT06090045.