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A1C Is a Predictor of Clinical Outcomes Following Noncardiac Surgery

Mar 14, 2014

Researchers discover that preoperative A1C is related to length of stay in the hospital following noncardiac surgeries…. 

Acute hyperglycemia at the time of surgery is associated with poor clinical outcomes in all patients. Furthermore, diagnosis of diabetes mellitus is known to be a risk factor for complications postoperatively. Some healthcare practitioners use insulin infusion protocols to provide better glycemic control and prevent hyperglycemia during and after surgery to help lower the risk of complications. Less is known about the effect of chronic hyperglycemia on surgical outcomes postoperatively, and whether addressing this issue prior to surgery would improve outcomes. A study was therefore designed to evaluate whether A1C impacts outcomes following surgery independent of any hyperglycemia that may occur perioperatively.

Data for this study was obtained from the National Surgical Quality Improvement Program database and from the data registry of the Brigham and Women’s Hospital. Data for patients having noncardiac surgery from 2005-2010 and requiring admission to the hospital for ≥1 day following surgery were included in this study. The 622 patients were divided into four groups based on their A1C levels. The groups were as follows: A1C≤6.5%, A1C 6.5-8%, A1C.8-10%, and A1C >10%. Patients were compared to nondiabetic control subjects of the same age, sex, and BMI.

The results of the data obtained showed patients with A1C 6.5-8% had a hospital LOS similar to the matched group of nondiabetic patients. Patients with an A1C≤6.5% or >8% had a hospital LOS that was significantly longer when compared to that of the matching nondiabetic patients. It may seem surprising that A1C≤6.5% was also associated with increased hospital LOS. It is thought that this could be occurring because these patients have an increased severity of underlying illness or have a greater occurrence of hypoglycemia. After adjusting for age, sex, BMI, race, surgery type, smoking status, glucose levels on the day of surgery, and results of the Charlson Comorbidity Index, statistical analyses showed higher A1C to be associated with increased hospital LOS following surgery.

This study was the first to show an independent relationship between A1C (demonstrating chronic glycemic control) and noncardiac surgical outcomes in diabetic patients. These results are important as more severe and prolonged hypoglycemia is more likely to result in damage than acute hyperglycemia. While other studies have shown higher A1C to be associated with increased risk for wound infections, acute renal failure, increased morbidity and other complications, this study differs in that it controlled for multiple risk factors and shows a threshold A1C level at which the risk of surgical complications increases. Currently, in most practices, a single blood glucose level on the day of surgery is used to determine blood glucose management, as practitioners are aware of the relationship between acute hyperglycemia and surgical outcomes. The results of this study suggest that chronic glycemic control is a better predictor of surgical outcomes and hospital LOS, and that this should be accounted for when treating the patient. As there are no current standards of care regarding A1C levels before surgery, practitioners vary in the cutoffs they use to determine increased risk.

The results of this study suggest that an A1C >8% can be used as a threshold for increased post surgery complications until further research is done. Future research should focus on evaluating other surgical outcomes besides hospital LOS, such as mortality, infections, renal failure, and rehospitalization rates. Also, research regarding whether improving A1C levels before surgery improves these outcomes would be beneficial.

Practice Pearls:
  • Preoperative A1C >8% and A1C≤6.5% are associated with increased hospital LOS following surgery.
  • Preoperative interventions to improve glycemic control in individuals with these A1C’s may improve outcomes.

Diabetes/Metabolism Research and Reviews 2014. Underwood, P. et al. "Preoperative A1C and Clinical Outcomes in Patients With Diabetes Undergoing Major Noncardiac Surgical Procedures" Diabetes Care. 2014;37: 611-616.