Systematic immunological evaluation in adult patients with inflammatory bowel disease

BACKGROUND: Inflammatory bowel disease (IBD) has been frequently reported in patients with primary immunodeficiency; however, the frequency and pattern of immunological abnormalities among adult patients with established IBD remain insufficiently characterized. We aimed to systematically evaluate immunological parameters in adult patients with established IBD. Additionally, we sought to identify clinical factors associated with laboratory-defined immunological deviations. METHODS: In this retrospective observational cohort study, we analyzed 108 adults with Crohn's disease or ulcerative colitis who underwent structured immunological evaluation as part of routine clinical care between 2011 and 2015 (a period of standardized screening). We excluded patients with major causes of secondary immunodeficiency (e.g., advanced renal failure, HIV infection, severe malnutrition). However, we recorded exposure to medications that could potentially cause secondary immunosuppression. The predefined laboratory panel included serum immunoglobulins, vaccine antibody responses, isohemagglutinin titers (not assessed in blood group AB), peripheral lymphocyte subsets (reported as percentages), and neutrophil phagocytic function, interpreted using standardized reference ranges. Immunological findings were categorized according to the IUIS 2025 phenotypic framework. Multivariable logistic regression was performed to assess factors associated with laboratory-defined immunological deviations. RESULTS: Clinically significant immunological disorders were identified in 12 patients (11.1%), and laboratory-defined (defined as combined defects across immune compartments) immunological deviations in 60 patients (55.6%). Reduced CD19⁺ B-cell percentages were observed in 45 patients (42.1%) and decreased NK cell percentages in 17 patients (15.9%). In multivariable analysis, increasing age (OR 1.064 per year; 95% CI 1.029-1.100; p < 0.001) and male sex (OR 3.61; 95% CI 1.32-9.87; p = 0.012) were independently associated with laboratory-defined immunological deviations; medication exposure showed a borderline association (OR 2.78; 95% CI 0.99-7.76; p = 0.052). CONCLUSIONS: In this adult IBD cohort evaluated using a structured laboratory framework, measurable immune alterations were common, although most did not meet criteria for clinically significant immunological disorders. These findings highlight immune heterogeneity in adult IBD and support further prospective studies with longitudinal outcomes to clarify the clinical implications and to define which patient subgroups may benefit from targeted immunological assessment.