Association of Early Postoperative Biochemical Markers with a Composite Adverse Perioperative Outcome After Bariatric Surgery

Background/Objectives: Bariatric surgery is the most effective treatment for sustained weight loss; however, early postoperative complications remain a significant concern. Routine biochemical markers obtained in the immediate postoperative period may enable early risk stratification, yet their prognostic value remains incompletely defined. This study aimed to evaluate the association between early postoperative biochemical alterations and composite adverse outcomes after bariatric surgery. Methods: In this retrospective observational study, 260 adult patients undergoing elective bariatric surgery were included. Preoperative and postoperative day 1 (POD1) laboratory parameters were retrieved from electronic medical records. The primary endpoint was a composite adverse outcome comprising postoperative intensive care unit admission, infection, anastomotic leak, or 30-day readmission. Univariable and multivariable logistic regression analyses were performed to evaluate independent associations, and receiver operating characteristic (ROC) curve analysis was used to assess discriminative performance. Results: Composite adverse outcomes occurred in 51 patients (19.6%). In multivariable analysis, longer operative duration (OR 1.17 per 10 min, 95% CI 1.04–1.31; p = 0.009), POD1 AST (OR 1.15 per 10 U/L, 95% CI 1.07–1.24; p < 0.001), and POD1 lactate-to-albumin ratio (LAR ×100) (OR 1.20, 95% CI 1.04–1.38; p = 0.014) were independently associated with adverse outcomes. POD1 AST demonstrated the highest discriminative ability (AUC 0.733), followed by glucose (AUC 0.688) and ALT (AUC 0.680), whereas LAR showed limited stand-alone performance (AUC 0.594). Conclusions: Longer operative duration and higher POD1 AST and LAR levels were independently associated with the composite adverse perioperative outcome. AST showed the highest, although moderate, individual discrimination, whereas LAR demonstrated limited stand-alone performance. Because immediate postoperative ICU transfer preceded POD1 biomarker sampling and dominated the composite outcome, these findings should be interpreted as associations rather than prospective prediction.