Nonlinear Association of Preoperative HbA1c With 30‑Day Complications After Inguinal Hernia Mesh Repair and Effect Modification by Day‑of‑Surgery Hyperglycemia

BACKGROUND: Whether chronic glycemic control relates nonlinearly to outcomes after inguinal hernia mesh repair and whether day-of-surgery hyperglycemia modifies risk remains uncertain. We assessed the continuous hemoglobin A1c (HbA1c)-risk curve for 30-day complications and 1-year recurrence. METHODS: We performed a single-center prospective cohort of adults undergoing elective inguinal hernia mesh repair from January 2017 to December 2023. Exposures were preoperative HbA1c within 30 days (continuous; <5.7%, 5.7% to 6.4%, 6.5% to 7.9%, ≥8.0%) and day-of-surgery glucose (DOS-BG) ≥180 versus <180 mg/dL. Analyses used multivariable logistic regression with restricted cubic splines, HbA1c×DOS-BG interaction testing, prespecified confounder adjustment, and multiple imputation, and Cox models for recurrence. RESULTS: We analyzed 3420 procedures; DOS-BG ≥180 mg/dL occurred in 22.0%. The 30-day composite occurred in 315 (9.2%). HbA1c was nonlinearly associated with risk (p_nonlin=0.008): relative to <5.7%, aORs were 1.11 (95% CI: 0.89-1.38), 1.38 (1.04-1.83), and 1.92 (1.31-2.81) for 5.7% to 6.4%, 6.5% to 7.9%, and ≥8.0%, respectively. DOS-BG ≥180 mg/dL was associated with higher modeled risk (aOR: 1.41, 1.14-1.74) and modified the HbA1c effect (p_interaction=0.03). Adjusted risks were 6.8% at HbA1c 5.5% and 11.6% at 8.5% with DOS-BG <180 mg/dL, versus 10.2% and 17.5% with DOS-BG ≥180 mg/dL. At 1 year, 55 recurrences/reoperation events (1.6%) occurred (KM: 1.7%, 95% CI: 1.3-2.2); adjusted hazards increased modestly with HbA1c (ordered trend P=0.08). CONCLUSIONS: Preoperative HbA1c relates nonlinearly to 30-day complications, and day-of-surgery hyperglycemia was associated with higher modeled risk across the HbA1c range. Findings support continuous HbA1c-based risk stratification. However, specific optimization thresholds require external validation.