Serum Immunoglobulin Levels and One-Year Mortality in Non-Cystic Fibrosis Bronchiectasis

<title>Abstract</title> <p> <bold>Background</bold> Bronchiectasis is a heterogeneous chronic airway disease associated with substantial morbidity and mortality. We investigated the associations of serum immunoglobulin levels with disease severity and one-year mortality and evaluated the incremental prognostic value of serum IgM beyond established prognostic models. <bold>Methods</bold> This retrospective single-center cohort study included 68 patients with non-cystic fibrosis bronchiectasis with available serum immunoglobulin measurements, sputum culture results, and at least one year of follow-up. Disease severity was assessed using the Bronchiectasis Severity Index (BSI), FACED, and E-FACED scores. Univariable and multivariable Cox proportional hazards regression analyses identified independent predictors of one-year mortality. Receiver operating characteristic (ROC) analysis evaluated the incremental predictive value of serum IgM when added to the E-FACED score. <bold>Results</bold> During one year of follow-up, 15 patients (22.1%) died. Reduced serum IgM levels (HR 0.14, 95% CI 0.02–0.79; p = 0.02) and chronic <italic>Pseudomonas aeruginosa</italic> colonization (HR 21.41, 95% CI 1.49–307.15; p = 0.02) were independently associated with mortality. The E-FACED score showed an AUC of 0.761, whereas the combined E-FACED–IgM model improved the AUC to 0.841, with higher sensitivity (78.6% vs. 53.3%), negative predictive value (92.8% vs. 86.0%), and overall accuracy (80.9% vs. 77.3%). <bold>Conclusions</bold> Reduced serum IgM independently predicted one-year mortality and improved the prognostic performance of the E-FACED score beyond established clinical risk factors. Incorporating serum IgM into the E-FACED score improved mortality prediction, suggesting that serum IgM may represent a readily available prognostic biomarker for risk stratification. Further multicenter prospective studies are warranted. </p>