Elevated preoperative red cell distribution width and incident infection after metabolic and bariatric surgery: a cohort study.

INTRODUCTION: Red cell distribution width (RDW), an index of erythrocyte size variability associated with inflammation and nutritional status, may have prognostic utility; however, its role in predicting infection after metabolic and bariatric surgery (MBS) remains unclear. METHODS: This TriNetX retrospective cohort study included adults undergoing primary MBS from 2010-2025. Elevated preoperative RDW was defined as ≥14.6% across all measurements within 3 months before surgery, while normal RDW ranged from 11.5 to 14.5%. Patients with discordant values were excluded. One-to-one propensity score matching was performed. The primary outcome was incident sepsis within 1 year, and secondary outcomes included pneumonia, surgical site infection (SSI), urinary tract infection (UTI), and intensive care unit (ICU) admission. RESULTS: After matching, 17,735 patients were included in each group. Elevated RDW was associated with an increased risk of sepsis (hazard ratios [HRs] 1.42, 95% confidence interval [CI] 1.15-1.75; p = 0.001), pneumonia (HR 1.33; p = 0.003), and ICU admission (HR 1.22; p = 0.018), but not UTI or SSI. Temporal analysis showed that the risk of pneumonia was highest early postoperatively, whereas the risk of sepsis increased over time. These associations persisted across surgical subtypes and were not fully explained by baseline anemia. Elevated RDW was also associated with subsequent iron deficiency (ferritin< 30 ng/mL) and inflammation markers (C-reactive protein >10 mg/L). CONCLUSION: Elevated preoperative RDW is associated with distinct temporal patterns of increased 1-year sepsis and pneumonia risks after MBS. RDW may serve as a simple, low-cost biomarker for perioperative risk stratification. Further prospective studies are warranted.