Clinical and Laboratory Factors Associated with Serious Infections in Multiple Myeloma: A Real-World Study

Background: Serious infections remain a major cause of morbidity and treatment disruption in patients with multiple myeloma (MM). Identifying readily available clinical factors associated with infectious complications may facilitate risk-adapted supportive care. This study evaluated clinical and laboratory factors associated with serious infection in patients with MM, including the potential association of baseline neutrophil-to-lymphocyte ratio (NLR) with subsequent serious infectious complications. Methods: This retrospective multicenter cohort study included 104 patients with MM. Baseline demographic, disease-related, treatment-related, and laboratory characteristics were evaluated. Serious infection was defined as an infectious episode requiring hospitalization. Infectious events were recorded throughout follow-up, including those occurring during second-line and subsequent therapies. Associations with serious infection were assessed using univariate and multivariable binary logistic regression analyses. The primary multivariable model included age, International Staging System (ISS) stage, dialysis requirement at diagnosis, treatment response, and baseline NLR. Results: Serious infections occurred in 39 patients (37.5%). Dialysis requirement at diagnosis (30.8% vs. 4.6%, p = 0.001), failure to achieve treatment response (51.3% vs. 7.7%, p < 0.001), hypogammaglobulinemia (48.7% vs. 29.2%, p = 0.046), and IVIG administration (76.9% vs. 46.2%, p = 0.002) were more frequent among patients with serious infection. Baseline NLR did not differ significantly between patients with and without serious infection. In the multivariable model, dialysis requirement at diagnosis (adjusted OR 8.26, 95% CI 1.81–37.68; p = 0.006) and failure to achieve treatment response (adjusted OR 16.77, 95% CI 4.37–64.31; p < 0.001) were independently associated with serious infection, whereas age, ISS stage, and baseline NLR were not. Conclusions: Serious infections were common in this real-world MM cohort. Dialysis requirement at diagnosis and failure to achieve treatment response were independently associated with serious infection, whereas baseline NLR was not independently associated with serious infectious complications. These findings suggest that clinical characteristics reflecting renal dysfunction and treatment response may be useful for identifying patients at increased risk of serious infection. The observed association between IVIG administration and serious infection should be interpreted cautiously because of potential confounding by indication and reverse causality.