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A1c Crucial Prior to Any Surgery

Apr 14, 2018

Study finds higher hospital admissions, complications, and mortality rates among patients with increased A1c.

With 30.3 million in the U.S. with diabetes and another 84.1 million with prediabetes, it is crucial to test for A1c to determine their possible risk for complications post operatively.  A study in Diabetes Care found that surgical in-patients with diabetes age 54 or older had longer hospital stays and increased rates of ICU admissions, major complications, mechanical ventilation and six-month mortality. The study of 7,565 people found the risk of adverse outcomes was associated with elevated A1C levels.

In this prospective, observational study, they measured the HbA1c of surgical inpatients age ≥54 years between May 2013 and January 2016. Patients were diagnosed with diabetes if they had pre-existing diabetes or an HbA1c ≥6.5% (48 mmol/mol) or with prediabetes if they had an HbA1c between 5.7–6.4% (39–48 mmol/mol) and they were followed for 6-months.

Surgical procedures place physical stress on patients and can lead to morbidity and mortality. Patients with diabetes and hyperglycemia, measured by HbA1c, may be at particular risk for perioperative morbidity from diabetes related complications. Although diabetes has been associated with increased mortality and morbidity in the setting of cardiac surgery, this association in the noncardiac surgery setting is variable.

Inconsistency remains in both the reporting and the definitions of surgical complications and perioperative morbidity among studies, making it difficult to draw conclusions on the association between diabetes and postoperative complications. Furthermore, previous studies have used medical records alone to identify diabetes in surgical patients, which may fail to identify the up to 18% who may have diabetes. Studies investigating the association of HbA1c with surgical outcomes have shown conflicting results, with some demonstrating associations with higher mortality, infection, myocardial infarction, renal failure, cerebrovascular accident, major complications, and hospital length of stay (LOS) and others failing to observe such associations.

Most studies assessing the association of hyperglycemia and postoperative outcomes have focused on perioperative hyperglycemia by using blood glucose readings around the time of surgery. However, perioperative hyperglycemia is not an accurate indicator of diabetes status because it is affected by perioperative fasting and stress hyperglycemia from surgical trauma. Accordingly, in this prospective study, they used HbA1c to determine both presence of diabetes and severity of chronic preadmission glycemic status. They tested the hypothesis that diabetes, defined as a categorical variable, and HbA1c, defined as a continuous variable, carry an independent association with adverse outcomes after surgery.

The study looked at surgical inpatients admitted to the hospital during the period of May 6, 2013 to January 2016, as part of the process. All patients age 54 years or older without an HbA1c reading within the last 3 months were given an A1c test on admission.

As part of the Diabetes Discovery Initiative, patients with HbA1c of 8.3% (67 mmol/mol) were seen by an endocrinology advanced trainee who generated a personalized plan for glycemic control. Patients undergoing high-risk surgery, including cardiac, orthopedic, and general surgery, with HbA1c between 7.5% (58 mmol/mol) and 8.2% (66 mmol/mol) and patients with newly diagnosed diabetes were seen by the internal medicine advanced trainee.

From the results, it was observed that the higher HbA1c was independently associated with adverse postoperative outcomes, including 6-month mortality, major complications, ICU admission, mechanical ventilation, and hospital LOS. Analysis confirmed a higher risk of 6-month mortality with diabetes in conjunction with other risk factors. In contrast, they did not find a significant association between prediabetes and adverse postoperative outcomes.

The association between diabetes and LOS has been previously demonstrated in surgical patients and was confirmed in this study. The association between diabetes and mortality has been demonstrated in the cardiac and noncardiac surgery setting. The current study demonstrates that 6-month mortality is higher in patients with diabetes undergoing surgery. Mechanical ventilation was significantly increased with diabetes in the current study.

This study is the largest to assess the impact of HbA1c across a wide range of surgical specialties. They also found higher HbA1c to be associated with greater LOS. In the current study, it was demonstrated that higher HbA1c was associated with a higher rate of major complications.

From the results it was concluded that, in patients age 54 years, diagnosis of diabetes identifies those at higher risk of morbidity and mortality after surgery and implies that poor glycemic control before surgery, indicated by an elevated HbA1c, remains an important risk factor for adverse outcomes after surgery. Logically, therefore, patients with diabetes and especially those with high HbA1c should be triaged to pathways of care dedicated to higher-risk populations. Risks of excessively tight blood glucose control perioperatively should be considered, but controversy exists regarding glycemic targets in the intensive care setting. Finally, they found that prediabetes as defined by HbA1c levels is not a risk factor for adverse outcomes after surgery.

Practice Pearls:

  • The study tested the hypothesis that diabetes and HbA1c carry an independent association with adverse outcomes after surgery.
  • Poor glycemic control before surgery, indicated by an elevated HbA1c, remains an important risk factor for adverse outcomes after surgery.
  • Those with an elevated A1c prior to surgery have a higher 6-month mortality.


Diabetes Care 2018; Ogurtsova K, da Rocha Fernandes JD, Huang Y, et al. IDF Diabetes Atlas: global estimates for the prevalence of diabetes for 2015 and 2040. Diabetes Res Clin Pract 2017;128:40–50 2. Australian Bureau of Statistics (ABS). National Health Survey: First Results, 2014-15 [Internet], care.diabetesjournals.org Yong and Associates 7 2015. Available from http://www.abs.gov.au/ ausstats/abs@.nsf/mf/4364.0.55.001. Accessed 26 September 2017 3. Nanayakkara N, Nguyen H, Churilov L, et al. Inpatient HbA1c testing: a prospective observational study. BMJ Open Diabetes Res Care 2015;3: e000113 4.