Beyond HbA1c: Multivariate Clustering and Propensity-Weighted Analysis Identify High-Risk Patients with Diabetes Undergoing Bariatric Surgery

Introduction: Preoperative glycemic control is a key concern in bariatric surgery. However, the extent to which suboptimal HbA1c levels impact short-term postoperative morbidity remains uncertain. This study evaluated the association between preoperative HbA1c categories and 30-day postoperative morbidity in a large Middle Eastern bariatric surgery cohort, using propensity score weighting and unsupervised clustering to refine risk stratification. Methods: This retrospective cohort analysis included 1778 bariatric surgery patients operated between 2019 and 2024 at a tertiary referral center in the United Arab Emirates. Patients were stratified into two groups: controlled HbA1c (≤6.5%, n = 1557) and elevated HbA1c (>6.5%, n = 221). Baseline demographics, perioperative parameters, and 30-day outcomes were extracted from a prospectively maintained registry. Statistical analysis included inverse probability weighting using propensity scores to adjust for age, BMI, and sex. Principal component analysis (PCA) followed by K-means clustering was performed on age and HbA1c to identify multivariate patient subgroups. Both unweighted and weighted analyses were performed. Results: Elevated HbA1c patients were older than those with controlled HbA1c (43.2 ± 12.1 versus 34.6 ± 10.8 years, P < .001 unweighted; 43.2 ± 12.1 versus 42.1 ± 12.0 years, P = .364 weighted). BMI was modestly higher in the elevated group but not significant after weighting. Thirty-day complication rates were low across all groups. The highest risk was observed in patients >60 years with diabetes (8.1%), while patients ≤20 years had negligible complications. In adults 21–60 years, complication rates increased modestly with HbA1c (normal 3.9%–5.3%, prediabetes 3.9%–6.3%, diabetes 6.5%–8.6%). No deaths occurred. Other complications, including deep/organ-space SSI, pneumonia, pulmonary embolism, renal failure, myocardial infarction, transfusion, gastrointestinal bleeding, readmission, and reoperation, were rare and showed no significant differences across HbA1c strata (all P > .05). Conclusion: Elevated HbA1c was not an independent predictor of short-term morbidity after bariatric surgery. PCA-cluster analysis identified a distinct high-risk subgroup: older diabetic patients, who demonstrated the greatest vulnerability to short-term complications. These findings suggest that perioperative risk assessment should move beyond HbA1c cutoffs alone and incorporate multivariate patient profiling to guide individualized care.