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J Thorac Cardiovasc Surg 2008;136:631-640
© 2008 The American Association for Thoracic Surgery
Surgery for Acquired Cardiovascular Disease |
a Clinical Research Unit, Division of Cardiothoracic Surgery, Emory University School of Medicine, Atlanta, Georgia
b Department of Biostatistics, Rollins School of Public Health, Emory University School of Medicine, Atlanta, Georgia
c Division of Cardiothoracic Surgery, Oregon Health and Science University, Portland, Oregon
Received for publication May 8, 2007; revisions received January 12, 2008; accepted for publication February 7, 2008. * Address for reprints: Vinod H. Thourani, MD, 550 Peachtree Street, Crawford Long Hospital, 6th Floor, Medical Office Tower, Cardiothoracic Surgery, Atlanta, GA 30308. (Email: vinod.thourani{at}emoryhealthcare.org).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionConclusionsReferences |
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Methods: Of 3555 consecutive patients who underwent primary, elective coronary artery bypass grafting at a single academic center from April 1, 2002, to June 30, 2006, 3089 (86.9%) had preoperative hemoglobin A1c levels obtained and entered prospectively into a computerized database. All patients were treated with a perioperative intravenous insulin protocol. A multivariable logistic regression model was used to determine whether hemoglobin A1c, as a continuous variable, was associated with in-hospital mortality, renal failure, cerebrovascular accident, myocardial infarction, and deep sternal wound infection after coronary artery bypass grafting. Receiver operating characteristic curve analysis identified the hemoglobin A1c value that maximally discriminated outcome dichotomies.
Results: In-hospital mortality for all patients was 1.0% (31/3089). An elevated hemoglobin A1c level predicted in-hospital mortality after coronary artery bypass grafting (odds ratio 1.40 per unit increase, P = .019). Receiver operating characteristic curve analysis revealed that hemoglobin A1c greater than 8.6% was associated with a 4-fold increase in mortality. For each unit increase in hemoglobin A1c, there was a significantly increased risk of myocardial infarction and deep sternal wound infection. By using receiver operating characteristic value thresholds, renal failure (threshold 6.7, odds ratio 2.1), cerebrovascular accident (threshold 7.6, odds ratio 2.24), and deep sternal wound infection (threshold 7.8, odds ratio 5.29) occurred more commonly in patients with elevated hemoglobin A1c.
Conclusion: Elevated hemoglobin A1c level was strongly associated with adverse events after coronary artery bypass grafting. Preoperative hemoglobin A1c testing may allow for more accurate risk stratification in patients undergoing coronary artery bypass grafting.
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Introduction |
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Although the literature is replete with studies in patients undergoing coronary artery bypass grafting (CABG) comparing outcomes in diabetic patients versus nondiabetic patients,2-9 the impact of preoperative glucose control on outcomes has not been extensively studied.10 Previous studies have used methods of glucose control (ie, diet vs oral hypoglycemics vs insulin) as a means to stratify outcomes.2,3,7 Moreover, because a spot preoperative glucose level is highly variable, it is unclear whether these treatment strategies were effective in achieving acceptable diabetes control before CABG. This is in contrast with perioperative glucose control, which has a significantly favorable impact on postoperative outcomes.10-15
The American Diabetes Association has recommended the use of the blood hemoglobin A1c (HbA1c) level as a method of assessing long-term glycemic control in diabetic patients.16 HbA1c, also known as glycosylated hemoglobin, indicates a patient's blood glucose control during the previous 3 to 4 months. HbA1c is formed when glucose in the blood binds irreversibly to hemoglobin to form a stable glycated hemoglobin complex. Because the normal life span of red blood cells is 90 to 120 days, HbA1c will only be eliminated when red cells are replaced. Because red cell turnover is continuous and HbA1c is not affected by short-term glycemic lability, HbA1c allows better assessment of glucose control during a 3- to 4-month time period. The American Diabetes Association currently recommends that patients with diabetes achieve HbA1c levels less than 7%, which is associated with a lower risk of diabetes-associated complications.17,18
We previously reported the detrimental effects of diabetes on the outcomes after CABG; however, that study did not take into account the influence of preoperative blood glucose control.2 The current study was performed to more specifically evaluate the role of preoperative blood glucose control (using the surrogate HbA1c laboratory value) on in-hospital outcomes after primary, elective, isolated CABG. Therefore, the purpose of this study was to 1) assess whether elevated HbA1c can be used as a risk factor for morbidity and mortality after CABG; 2) determine whether patients with well-controlled diabetes preoperatively (HbA1c < 7%) had better outcomes compared with patients with poorly controlled diabetes preoperatively (HbA1c 
7%); 3) determine whether patients with well-controlled diabetes (HbA1c < 7%) have outcomes comparable to those without a history of diabetes; and 4) validate the American Diabetes Association recommended HbA1c thresholds and provide thresholds for previously unstudied adverse outcomes after CABG.
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Materials and Methods |
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Cardiopulmonary bypass (CPB) was used according to the discretion of the attending surgeon. Conventional CABG with CPB was performed with standard techniques, using roller head pumps, membrane oxygenators, cardiotomy suction, arterial filters, cold antegrade or retrograde blood cardioplegia, and moderate systemic hypothermia (32°C–34°C). Off-pump CABG was performed with one of several commercially available cardiac positioning and coronary artery stabilizing devices. Patients who were converted intraoperatively from off-pump CABG to conventional CABG were entered into the database and analyzed according to the operation they ultimately received.
All patients were treated with a uniform perioperative intravenous insulin protocol. In the operating room, an insulin infusion was premixed with 125 units of insulin in 250 mL 0.9% normal saline. Routine measurement of blood glucose was obtained from serial arterial blood gases measured every 30 minutes. In the intensive care unit, glucose levels were obtained from arterial blood gas samples or finger stick samples every 2 hours. Once patients were transferred to the floor, blood glucose values were obtained every 4 to 6 hours. Glucose levels were obtained via arterial samples in the operating room and the intensive care unit and via finger stick blood samples on the floor. The insulin infusion was initiated for blood glucose more than 120 mg/dL and adjusted to target intraoperative blood glucose between 80 and 110 mg/dL according to the discretion of the attending cardiac anesthesiologist. In the intensive care unit, patients received a continuous insulin infusion that was adjusted to maintain blood glucose between 80 and 110 mg/dL according to a sliding scale (blood glucose – 60 x 0.04 = units of insulin per hour). On transfer out of the intensive care unit, most patients are monitored with blood glucose monitoring every 4 to 6 hours (goal blood glucose < 150 mg/dL) and maintained according to the sliding scale with subcutaneous insulin in addition to their preoperative subcutaneous regimens. If necessary to achieve glucose control, continuous insulin infusion was continued after transfer out of the intensive care unit. Patients with newly diagnosed or poorly controlled diabetes also received endocrinology consultation for better control in the postoperative period. To adjust for the effect of perioperative glucose, 2 different mean glucose values were computed and modeled: the mean glucose value for the day of surgery and the mean glucose value for postoperative days 1 to 3. The blood glucose level was used as a continuous variable in the multivariable analysis.
Analytically, this study aimed to determine whether HbA1c was an independent risk factor of adverse outcomes. To this end, a total of 22 covariates were collected to use as risk adjustors to ensure that the effect of HbA1c was not confounded by their influence. These covariates are listed in Table 1
by HbA1c groupings (<7% and 7%). The HbA1c classifications were chosen according to recommendations of the American Diabetes Association, which recommends a target HbA1c of less than 7%.17,18 Race was modeled as a binary variable (caucasian or non-caucasian), as was New York Heart Association classification (class 4 or non-class 4), Canadian Cardiovascular Society classification (class 4 or non-class 4), and chronic lung disease (presence or absence). The outcomes collected for consideration were in-hospital mortality, renal failure, myocardial infarction (MI), cerebrovascular accident (CVA), deep sternal wound infection (DSWI), presence of any infection (superficial or DSWI, pneumonia or septicemia), atrial fibrillation, and postoperative length of stay (LOS).
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were used to impute missing values. The goal of multiple imputations is not to replace data with plausible values but rather to impute with values that will maintain the covariance structure so that valuable data that are not missing will not be omitted from analysis. Ten separate multiple imputations were generated (using PROC MI, SAS version 9.1, SAS Institute Inc, Cary, NC), and the results were combined (using PROC MIANALYZE) to evaluate all model terms. Separate multiple logistic regression models (one for each binary outcome) were constructed using HbA1c as the primary variable of interest and adjusting for the other 22 risk factors (Table 1). Of interest was whether HbA1c, modeled as a continuous factor, was predictive of adverse outcomes in the presence of diabetes status and other potential confounders. Adjusted odds ratios (ORs) were reported and measure the additional increase in odds of outcome per unit increase in HbA1c.
For each binary adverse event outcome, 2 models were constructed. The first type of model is an adjusted model (accounting for all of the covariates) and is designed to measure the association between HbA1c apart from the confounders. The second model is unadjusted and designed to measure the "pure" effect of HbA1c without any adjustors. To further evaluate the impact of HbA1c in explaining each outcome, the discrimination of these models was evaluated using the area under the receiver operating characteristic (AUROC) curve, a measure of discrimination. AUROC is estimated by the c-index, which was used for this study. Discrimination is the model's ability to distinguish between patients who have an event and patients who do not have an event. The AUROC ranges from 0.50 to 1.00; values closer to 0.50 indicate poor discrimination, and values closer to 1.00 indicate superior discrimination. Alternatively, AUROC may be thought of as the probability that a randomly selected patient who has an adverse event will have a higher predicted probability of exhibiting the event than a randomly selected unaffected patient. For each outcome and model, the AUROC was computed for the logistic regression model.
Of further interest was to identify the HbA1c threshold value that maximized the AUROC as a binary predictor of adverse outcomes. To evaluate this, HbA1c was constructed as a binary variable with a threshold that was continually shifted by increments of 0.1% units. Each time the threshold was shifted, the impact of the binary variable was reevaluated in both the unadjusted and adjusted logistic models. The threshold value whose resultant binary predictor maximized the AUROC was recorded for each adverse outcome in the unadjusted and adjusted models. The OR for the unadjusted and adjusted thresholds that maximized the AUROC was also computed and recorded.
LOS was examined with respect to continuous HbA1c using an adjusted general linear model (analysis of covariance approach). Partial tests were performed to test for a non-zero slope for the HbA1c term.
The data were managed and analyzed with SAS version 9.1. All statistical tests were evaluated using a 2-tailed .05 level of significance. Model terms and statistical comparisons were preplanned. The authors had full access to the data and take responsibility for its integrity. All authors have read and agree to the article as written.
Preoperative Definitions
Definitions for preoperative variables were according to the Society of Thoracic Surgeons National Database and are as follows: diabetes indicates a history of diabetes, regardless of duration of disease or need for antidiabetic agents; renal failure indicates whether a patient has a history of renal failure or a creatinine level greater than 2; stroke indicates whether a patient has a history of a central neurologic deficit lasting more than 72 hours; left main coronary disease indicates narrowing of the diameter of the lumen by more than 50% in the left main coronary artery; peripheral vascular disease indicates whether a patient has a history of claudication with exercise or rest, amputation for arterial insufficiency, vascular surgery or percutaneous vascular intervention, or abdominal aortic occlusion or aneurysm; chronic lung disease is determined by forced expiratory volume in 1 second, history of inhaled or oral bronchodilator therapy, use of steroids aimed at treating lung disease, and PAO
2 and PACO
2 levels; arrhythmia indicates a history of arrhythmia (atrial fibrillation/flutter, ventricular tachycardia/fibrillation, third-degree heart block) that has been documented and treated; hypertension is documented as history of hypertension treated with medication, diet, or exercise, or systolic blood pressure greater than 140 or diastolic blood pressure greater than 90 on 2 separate occasions, or currently receiving antihypertensive medication. Canadian Cardiovascular Society classification was used to define angina and the New York Heart Association criteria (The Criteria Committee) were used to define congestive heart failure.
Postoperative Definitions
Definitions for postoperative outcomes were also according to the Society of Thoracic Surgeons National Database and are as follows: in-hospital death indicates whether a patient died during the hospitalization in which CABG was performed; renal failure indicates acute renal failure in which serum creatinine was elevated more than 2.0 and 2 times the most recent preoperative creatinine level; MI indicates a creatine kinase-MB elevation 5 or more times the upper limit of normal and presence of Q waves in 2 or more contiguous ECG leads during the initial 24 postoperative hours, or evolutionary ST-segment changes or new left bundle branch block or the aforementioned criteria after the initial 24 postoperative hours; CVA indicates whether a patient had a central neurologic deficit persisting more than 72 hours (permanent stroke), transient ischemic attack, deficit resolving within 24 hours, or deficit lasting more than 24 hours but less than 72 hours (reversible ischemic neurologic deficit); DSWI indicates whether a patient had an infection involving muscle, bone, or mediastinum requiring operative intervention; atrial fibrillation indicates whether a patient developed new-onset atrial fibrillation in the postoperative setting. In addition to these complications, we included a composite of infection index that included the presence of any sternal wound infection (deep or superficial), pneumonia, or septicemia.
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Results |
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7%). Beginning in 2002, as part of our routine preoperative labs, we obtained preoperative HbA1c levels in all patients undergoing elective CABG. The lack of uniform adoption of this screening method until July of 2002 accounts for the fact that only 87% of patients had HbA1c levels obtained during the study period. Preoperative demographics, clinical variables, and perioperative factors comparing patients with HbA1c greater than or less than 7 are listed in Table 1. Forty-two percent (516/1240) of diabetic patients were well-controlled with HbA1c levels less than 7%. Of note, 4.9% (90/1849) of patients without a history of diabetes had HbA1c levels of 7% or greater, suggesting undiagnosed and/or untreated diabetes mellitus. Similarly, 11% (90/814) of patients with HbA1c levels of 7% or greater had no history of diabetes. Most patients in this study had multivessel coronary disease, more than 95% of patients received arterial grafting with the left internal thoracic artery or bilateral internal thoracic artery grafting, and the majority of cases were performed without the use of CPB. The mean glucose values for the day of surgery (r = 0.37) and postoperative days 1 to 3 (r = 0.40) were both moderately correlated with preoperative HbA1c values.
Unadjusted Outcomes
In-hospital outcomes are summarized by HbA1c subgroup in Table 2
. For all patients (N = 3089), the overall incidence of major adverse events (death, CVA, or MI) was low (3.0%). All outcomes were significantly worse in those patients with HbA1c levels of 7% or more, with the exception of postoperative MI and atrial fibrillation. The preoperative method of glucose control for patients with a history of diabetes was also significantly different between groups (P = .006). In diabetic patients with HbA1c less than 7%, glucose was controlled with diet alone in 20.5% (106), oral hypoglycemic medications in 58.7% (303), and subcutaneous insulin in 18.8% (97). In diabetic patients with HbA1c of 7% or more, glucose was controlled with diet alone in 10.5% (76), oral hypoglycemic medications in 51.5% (373), and subcutaneous insulin in 37.9% (275). Patients who were managed with a combination of oral hypoglycemic medications and subcutaneous insulin therapy were grouped into those who received subcutaneous insulin. Pre- and postoperative treatment with aspirin, beta-blockers, and statins were not significantly between HbA1c groups. Preoperatively, approximately 77% of patients received aspirin, 70% of patients received beta-blockers, and 21% of patients received statins. Angiotensin-converting enzyme inhibitors were used more often in patients with HbA1c of 7% or more (38.6% vs 32.3%, P = .001). Postoperatively, approximately 93% of patients received aspirin, 93% of patients received beta-blockers, and 90% of patients received statins. Angiotensin-converting enzyme inhibitors were used more often in patients with HbA1c of 7% or more (43.8% vs 32.1%, P < .001). Of the 18 deaths in patients with HbA1c less than 7%, 10 were cardiac related and 8 were due to various causes (intraoperative [1], multisystem organ failure [2], pulmonary [3], renal failure [1], stroke [1]). Of the 13 deaths in patients with HbA1c of 7% or more, 9 were cardiac related. One patient died of complications of stroke, and 3 patients died of pulmonary complications. There were 34 of 1648 patients (2.1%) with HbA1c less than 7% and 9 of 540 patients (1.7%) with HbA1c of 7% or greater who were converted from off- to on-pump CABG. There were 4 deaths in the group with HbA1c less than 7% and 0 deaths in the group with HbA1c of 7% or more.
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7%) (Table 4
). The incidence of adverse events was significantly higher for the patients with uncontrolled diabetes (HbA1c 7% group), including renal failure (P = .028), DSWI (P = .007), and the composite index of infection (0.069). Although there was a trend toward more mortality in patients with uncontrolled diabetes (1.4%) compared with those with controlled diabetes (0.6%), this did not reach statistical significance.
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Discussion |
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In this study, 1240 of 3089 patients (40%) presented with a history of diabetes mellitus. Even within the Emory Healthcare System, we have seen an increase in diabetic patients referred for surgical revascularization. In our previous report,2 only 19% of patients undergoing CABG from 1978 to 1993 had a history of diabetes mellitus. According to the Bypass Angioplasty Revascularization Investigation, patients with multivessel disease had improved survival when treated with an initial strategy of CABG versus percutaneous intervention.20 Therefore, we expect a larger proportion of patients with multivessel coronary disease to be referred for surgical revascularization.
Recent studies comparing diabetic and nondiabetic patients after CABG have yielded conflicting results regarding in-hospital and short-term outcomes. Calafiore and colleagues6 showed that diabetes was an independent risk factor for early cardiac death only and not for all-cause mortality. Rajakaruna and associates5 found in a risk-adjusted analysis that diabetic patients had mortality outcomes comparable to those of nondiabetic patients. Kubal and coworkers7 showed that insulin-dependent diabetic patients had an increased risk of postoperative morbidity, but that just the history of diabetes was not associated with increased mortality. Other studies have refuted these claims, including work by Carson and colleagues,3 Thourani and colleagues,2 and Woods and colleagues.4 In several of these studies, the mode of glycemic control was used to stratify diabetic patients into those with glucose controlled with oral hypoglycemic medications versus insulin therapy,2,7 as well as those with other complications of diabetes, such as renal failure and peripheral vascular disease.21 The largest study to date by Carson and colleagues3 examined outcomes in 41,663 diabetic patients compared with 105,123 nondiabetic patients and found that patients with diabetes had a 23% to 37% increase in 30-day mortality and in-hospital morbidity compared with patients without diabetes. Some of these differences may be explained by how diabetic patients were defined. For example, exclusion of those with diet-controlled diabetes or exclusion of those without a preoperative history of diabetes (which may have occurred in retrospective analyses) may alter the comparisons between groups.
The practice changes in the past decade compared with earlier reported studies may also have affected the lack of a mortality difference between diabetic and nondiabetic patients. Specifically, the routine use of the left internal thoracic artery,22 improvements in anesthesia and critical care, the use of off-pump CABG techniques, perioperative insulin infusion,10-15 and improved secondary prevention protocols,23 including antiplatelet medication, lipid-lowering regimens, and preoperative glucose modulation with insulin and oral hypoglycemic regimens, may have collectively improved outcomes in diabetic patients undergoing CABG. These differences may make interpretation of older studies24-28 less reliable compared with current reports. In the present study, we sought to determine whether these outcome differences could be explained by preoperative glycemic control (as measured by HbA1c) rather than the mere history of diabetes mellitus.
One of the most dramatic improvements in outcomes among diabetic patients has been the implementation of tight perioperative glucose control. Furnary and colleagues10,14,15 reported dramatic reductions in mortality and DSWI among diabetic patients (comparable to nondiabetic patients) managed with a continuous insulin infusion initiated intraoperatively and maintained through the first 2 postoperative days. The authors attributed these improvements to enhanced myocardial glycometabolic function associated with euglycemia achieved by continuous insulin infusion. We aimed to regulate glucose levels between 80 and 110 mg/dL in all patients in the operating room and in the intensive care unit using a continuous insulin infusion. Once patients were transferred to the telemetry unit, management was variable and dependent on their control in the intensive care unit. This included the use of continuous insulin infusion, scheduled subcutaneous insulin therapy, and a sliding scale. Although patients with preoperative HbA1c 7% or more had significantly higher intra- and postoperative mean glucose levels compared with patients with HbA1c less than 7%, the mean glucose levels in patients with HbA1c 7% or more (day 0: 143 mg/dL, days 1–3: 154 mg/dL) were comparable to those of diabetic patients in other studies.10-15 Although we did not achieve the desired target blood glucose levels in the operating room and intensive care unit, perioperative glucose control was reasonable. In addition, preoperative HbA1c level still emerged as an independent predictor of mortality and DSWI after CABG in the multivariate analysis, even after adjusting for mean glucose levels on the day of surgery and the first 3 postoperative days. This is in contrast with the findings of Furnary and Wu,10 which did not identify HbA1c as a risk factor. Therefore, we agree with previous authors that strict intraoperative and postoperative glucose control is imperative to minimize both postoperative morbidity and mortality after CABG. However, it is plausible from these data that HbA1c is also an independent predictor of postoperative adverse events that is not entirely due to intra- and postoperative glucose control. This is most likely explained by the associated comorbidities that patients with long-standing diabetes present with before CABG, including renal insufficiency, cerebrovascular disease, hypertension, and more advanced coronary artery disease as seen in the preoperative comorbidities in our patients with elevated HbA1c. In addition to predicting adverse events, it may be more difficult to achieve intra- and postoperative euglycemia in patients with elevated HbA1c. Therefore, more aggressive glucose management should be used in these patients in the perioperative period.
HbA1c reflects a patient's glucose control during the preceding 3 to 4 months. Current practice guidelines according to the American Diabetes Association recommend routine HbA1c screening of diabetic patients as frequently as every 3 months in patients with elevated A1c levels (7%) or in patients with medication adjustments to ensure an adequate treatment regimen.13 Current recommendations suggest that patients with diabetes aim to achieve HbA1c levels of at least less than 7%.17,18,29,30 We chose to order HbA1c for all patients starting in 2002 (even those without a history of diabetes) to determine whether this approach would identify patients who had uncontrolled hyperglycemia without a previous diagnosis of diabetes mellitus. As seen in Table 3, 90 patients in this study without a previous diagnosis of diabetes had preoperative HbA1c levels of 7% or greater. This prompted confirmatory diagnosis in the postoperative setting and endocrinology consultation for management of diabetes.
To our knowledge, this is one of the few studies that assessed whether HbA1c, the standard measure to assess long-term glucose control, is a potential risk factor for adverse outcomes in patients undergoing CABG.10 It is possible that a preoperative HbA1c level may provide more accurate prognostic information about outcomes after CABG compared with a diabetes status alone. In patients with diabetes but with good long-term preoperative glycemic control (HbA1c < 7%), outcomes (with the exception of the composite index of infection) were comparable to those of patients without a diagnosis of diabetes and with HbA1c less than 7%. In addition, we implemented continuous insulin infusion to achieve glucose control on the day of surgery and in the intensive care unit. This may have accounted for the lack of a mortality difference between diabetic patients and nondiabetic patients in the unadjusted analysis. Because other studies evaluating the impact of diabetes on morbidity and mortality after CABG have resulted in different conclusions, we hypothesize that some of these differences may in part be due to the lack of a standardized measure (HbA1c) to adjust for significant differences in long-term preoperative glycemic control. This would apply to all diabetic patients, irrespective of the mode of therapy used for glucose control, suggesting that some patients should begin more intense glucose control with insulin therapy before CABG. Moreover, in patients with HbA1c greater than 8.7% and not requiring an urgent or emergency CABG, consideration should be given to maximizing blood glucose control before surgery to minimize morbidity and mortality.
Limitations
Our study has the inherent biases of any retrospective review of a prospectively collected database. Although we controlled for multiple variables, there may still be confounding factors that may have altered the results. For instance, even though we controlled for perioperative glucose values in the multivariable analysis, it is possible that better glucose control in patients with an elevated HbA1c may have reduced adverse events in this group. Furthermore, although we endeavored to only use a limited set of confounders, for some outcomes with rare event rates (MI), the number of covariates might be disproportionately higher than the "rule of 10" (at least 10 events for every covariate added to a model) would suggest. Our study population may be different from those of other studies with regard to surgical approach and perioperative care. Approximately 70% of patients underwent CABG without the use of CPB. All patients were treated with a strict perioperative insulin infusion and then transitioned to subcutaneous insulin to target blood glucose less than 150 mg/dL. Although we used a multivariate analysis model, we did not use propensity matching in our subgroup analyses. The goal of propensity scoring is to identify whether some intervention is associated with an outcome while working to balance these intervention groups with respect to their other preoperative characteristics. The problem with propensity scoring in our present study is that there is no intervention; HbA1c is a pure preoperative risk factor and not any type of intervention. Furthermore, we did not determine whether insulin-dependent patients had worse outcomes compared with those with diabetes controlled with diet or oral hypoglycemic medications, as has been done in other studies. In this study, only patients who reported a history of diabetes preoperatively were classified as "diabetic." In this retrospective analysis, patients with no known history of diabetes were classified as "nondiabetic" even if they were determined to be diabetic in the postoperative period. In these patients, their diagnosis would have been overlooked without a preoperative HbA1c level.
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Footnotes |
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References |
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