The Presence of Diabetes and Higher HbA1c Are Independently Associated With Adverse Outcomes After Surgery

Abstract

OBJECTIVE Limited studies have examined the association between diabetes and HbA1c with postoperative outcomes. We investigated the association of diabetes, defined categorically, and the association of HbA1c as a continuous measure, with postoperative outcomes. RESEARCH DESIGN AND METHODS In this prospective, observational study, we measured the HbA1c of surgical inpatients age ≥54 years at a tertiary hospital between May 2013 and January 2016. Patients were diagnosed with diabetes if they had preexisting diabetes or an HbA1c ≥6.5% (48 mmol/mol) or with prediabetes if they had an HbA1c between 5.7 and 6.4% (39 and 48 mmol/mol). Patients with an HbA1c <5.7% (39 mmol/mol) were categorized as having normoglycemia. Baseline demographic and clinical data were obtained from hospital records, and patients were followed for 6 months. Random-effects logistic and negative binomial regression models were used for analysis, treating surgical units as random effects. We undertook classification and regression tree (CART) analysis to design a 6-month mortality risk model. RESULTS Of 7,565 inpatients, 30% had diabetes, and 37% had prediabetes. After adjusting for age, Charlson comorbidity index (excluding diabetes and age), estimated glomerular filtration rate, and length of surgery, diabetes was associated with increased 6-month mortality (adjusted odds ratio [aOR] 1.29 [95% CI 1.05–1.58]; P = 0.014), major complications (1.32 [1.14–1.52]; P < 0.001), intensive care unit (ICU) admission (1.50 [1.28–1.75]; P < 0.001), mechanical ventilation (1.67 [1.32–2.10]; P < 0.001), and hospital length of stay (LOS) (adjusted incidence rate ratio [aIRR] 1.08 [95% CI 1.04–1.12]; P < 0.001). Each percentage increase in HbA1c was associated with increased major complications (aOR 1.07 [1.01–1.14]; P = 0.030), ICU admission (aOR 1.14 [1.07–1.21]; P < 0.001), and hospital LOS (aIRR 1.05 [1.03–1.06]; P < 0.001). CART analysis confirmed a higher risk of 6-month mortality with diabetes in conjunction with other risk factors. CONCLUSIONS Almost one-third of surgical inpatients age ≥54 years had diabetes. Diabetes and higher HbA1c were independently associated with a higher risk of adverse outcomes after surgery.