Long-Term Glucose Control as Measured by Hemoglobin ALC Predicts
Preoperative Fasting Blood Glucose
Vivek K. Moitra, M.D., Jason Greenberg, M.D., Bobbie Jean Sweitzer, M.D., Melinda Drum, M.D., Ph.D.
Department of Anesthesiology and Critical Care, University of Chicago Hospitals, Chicago, IL

Introduction
Glycemic control during the perioperative period is challenging because multiple factors affect blood sugar, including the stress of surgery, acute illness, anorexia, and NPO status. Various studies have examined the relationship of fasting plasma glucose to glycosylated hemoglobin.1 To our knowledge, there are no data on the use of HbA1c to predict glucose control in fasting patients during the perioperative period. Our study examined the predictive value of long-term glucose control to preoperative glucose values.

Methods
After IRB approval patients were recruited and consented in an outpatient preoperative clinic. 186 patients were analyzed in a prospective observational study. HbA1c values were drawn within three months of surgery followed by a preoperative blood sugar on the day of surgery. The relationship between preoperative fasting glucose levels and HgbA1c was evaluated using multivariable linear regression with glucose level as the dependent variable and HgbA1c as the primary explanatory variable, controlling for age, sex, race and BMI. This preliminary analysis excluded patients who had taken morning insulin, steroids or hypoglycemic agents on the day of surgery.

Results
HbA1c is a highly significant predictor of preoperative glucose levels, with glucose levels increasing by 20 units for each 1 unit increase of HbA1c. However, there was considerable variability in fasting glucose and only 21% of the variability could be explained by HbA1c (R2 = 0.2145). The patient characteristics that were considered did not modify the relationship between glucose and HbA1c, and were not statistically significant predictors of glucose levels after controlling for HbA1c, with the exception of age. In the multivariable model, a one-year increase in age corresponded to a small increase in preoperative glucose
(s.e. = 0.29, p-value = 0.031).

Conclusions
Glucose normalization in diabetic patients undergoing surgery lowers the risk of complications such as infection and wound healing.2 HbA1c values predict and contribute to preoperative fasting blood glucose levels drawn on the day of surgery and may be used to determine which patients are at higher risk for poor glucose control in the perioperative period. As anesthesiologists adjust preoperative diabetic management in the outpatient setting, we believe these data may be useful in stratifying therapies and preventing
episodes of hypoglycemia or hyperglycemia.

1 Woerle HJ, Pimenta WP, Meyer C, et al. Diagnostic and therapeutic implications of relationships between fasting 2-hour postchallenge plasma glucose and hemoglobin A1c values. Arch Intern Med 2004; 164: 1627-1632.
2 Golden SH, Peart-Vigilance C, Kao WH, Brancati FL. Perioperative glycemic control and the risk of infectious complications in a cohort of adults with diabetes. Diabetes Care 1999; 22: 1408-14.

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