Comparative analysis of demographic and clinical features in common variable immunodeficiency and selective immunoglobulin G deficiency

<b>Background:</b> Common variable immunodeficiency (CVID) and selective immunoglobulin G (IgG) deficiency (sIgGD) are primary antibody deficiencies with divergent clinical trajectories. CVID is characterized by recurrent infections and systemic noninfectious complications, whereas sIgGD typically follows a milder course. Despite sharing clinical features such as recurrent infections, comparative data on complications and mortality remain limited, which hinders risk-stratified management. <b>Objective:</b> This study compared the prevalence, clinical impact, and mortality associated with noninfectious complications in CVID and sIgGD, and identified predictors of adverse outcomes to support risk-stratified management and examined clinical differences within the CVID group based on baseline serum IgM levels. <b>Methods:</b> A single-center retrospective cohort study (2018-2024) included 111 patients with CVID and 19 patients with sIgGD. Diagnostic criteria for CVID included hypogammaglobulinemia (IgG level < 400 mg/dL with low IgA/IgM), impaired vaccine responses, and exclusion of secondary causes. The sIgGD required isolated IgG deficiency with normal IgA/IgM and intact vaccine responses. Noninfectious complications, including organ-specific and systemic manifestations as well as bronchiectasis were evaluated. In patients with CVID, a predefined subgroup analysis was performed based on baseline serum IgM levels (normal versus <40 mg/dL). Multivariate logistic regression identified mortality predictors. <b>Results:</b> The patients with CVID exhibited significantly higher rates of recurrent sinopulmonary infections (70.3% versus 42.1%), bronchiectasis (46.8% versus 21.1%), and noninfectious complications (57.7% versus 31.6%), including autoimmune disorders such as hematologic manifestations (33.3% versus 10.5%). In the CVID group, the patients with low IgM levels exhibited a significantly higher prevalence of gastrointestinal involvement (24.0% versus 5.6%; p = 0.035). Bronchiectasis (odds ratio [OR] 5.22) and noninfectious complications (OR 7.95) independently predicted mortality in CVID. Male sex showed borderline risk. In contrast, no mortality was observed in the sIgGD cohort over the study period. <b>Conclusion:</b> CVID is associated with substantial noninfectious morbidity and mortality, which necessitates early identification and long-term monitoring. In contrast, sIgGD exhibits a milder clinical phenotype, although preventive care remains important. These findings support distinct management strategies and highlight the utility of clinical markers for risk stratification.