People with diabetes are more likely to require surgery due to the complications that can result from the condition.1-3 Whilst there is substantial evidence that diabetes increases the risk of morbidity and mortality after major surgery,4-10 literature is conflicting on whether elevated preoperative haemoglobin A1c (HbA1c) levels, a measure of glycaemic control, is associated poorer postoperative outcomes.11-16
The aim of this systematic review is to investigate the effect of incremental increases in preoperative HbA1c levels and their impact on incidence of postoperative complications in adult patients undergoing major non-cardiac surgery.
We systematically searched EMBASE, MEDLINE and the Cochrane Library databases to identify eligible studies published between January 2012 and July 2023. Studies which measured HbA1c within 6 months before surgery and analysed it as a continuous variable or compared outcomes between at least three incremental subgroups were included.
Twenty observational studies (108,005 patients) from various surgical specialties were included in the review. Patients with higher preoperative HbA1c levels had higher odds of overall postoperative complications, postoperative acute kidney injury, anastomotic leak, surgical site infections and increased length of stay. There were no significant differences in the incidence of reoperations and mortality within 30 days of surgery between HbA1c subgroups. The literature was highly variable with respect to composite major complications, perioperative cardiovascular events, hospital readmissions, postoperative infections, pneumonia and systemic thromboembolism.
Conclusion: There appears to be a trend between higher preoperative HbA1c levels and increased incidence of postoperative complications in patients undergoing major non-cardiac surgery. High quality evidence from prospective studies is lacking, with many of the included studies lacking adequate statistical power to detect differences at an individual outcome level. Larger prospective studies are needed to confirm if the risks posed by high preoperative HbA1c levels warrant significant perioperative intervention.