Association between blood urea nitrogen and prognosis in critical patients with multiple myeloma: a retrospective cohort study

Blood urea nitrogen (BUN) has been established as an independent prognostic factor in various diseases. However, its prognostic significance in critically ill patients with multiple myeloma (MM) remains unclear. This study aimed to evaluate the association between BUN levels and mortality risk in this population. This retrospective cohort study extracted data from the Medical Information Mart for Intensive Care (MIMIC-IV) version 2.2 database. Adult patients with a first ICU admission and a diagnosis of MM were included. The primary outcome was 28-day mortality; secondary outcomes were 90-day mortality and 365-day mortality. Cox proportional hazard regression models and Kaplan‒Meier survival analyses were used to evaluate the associations between BUN levels and patient prognosis. Subgroup and sensitivity analyses were conducted to assess the robustness of the findings. After full adjustment, each 5 mg/dL increase in BUN was associated with a 6% increase in 28-day mortality (hazard ratio [HR], 1.06; 95% confidence interval [CI], 1.01–1.11). Furthermore, elevated BUN levels (> 43 mg/dL) were found to be associated with an increased risk of 28-day mortality (HR, 6.36; 95% CI, 2.27–17.78) compared with the reference group (BUN levels < 24 mg/dL). Similar trends were observed for mortality at 90 and 365 days. Kaplan–Meier curves showed significantly lower survival probabilities with higher BUN levels (log-rank P < 0.001). Restricted cubic spline analysis revealed a non-linear relationship with an inflection point at 51.3 mg/dL. Elevated BUN levels within 24 h of first ICU admission is independently associated with short- and long-term mortality in critically ill patients with MM. BUN may serve as a simple and readily available biomarker for early risk stratification in this vulnerable population. Blood urea nitrogen (BUN) serves as a valuable indicator of disease outcomes; however, its prognostic utility in multiple myeloma (MM) remains unclear. This study investigated the impact of BUN levels on mortality risk among critically ill patients with MM, utilizing data from the MIMIC-IV database. The findings revealed that elevated BUN levels within 24 h of first ICU admission were significantly associated with adverse outcomes. Consequently, BUN may serve as a readily available prognostic marker for mortality in this specific patient population.