Hemoglobin A1c as a screen for previously undiagnosed prediabetes and diabetes in an acute-care setting

OBJECTIVE

Hemoglobin A_1c (HbA_1c) is recommended for identifying diabetes and prediabetes. Because HbA_1c does not fluctuate with recent eating or acute illness, it can be measured in a variety of clinical settings. Although outpatient studies identified HbA_1c-screening cutoff values for diabetes and prediabetes, HbA_1c-screening thresholds have not been determined for acute-care settings. Using follow-up fasting blood glucose (FBG) and the 2-h oral glucose tolerance test (OGTT) as the criterion gold standard, we determined optimal HbA_1c-screening cutoffs for undiagnosed dysglycemia in the emergency department setting.

RESEARCH DESIGN AND METHODS

This was a prospective observational study of adults aged ≥18 years with no known history of hyperglycemia presenting to an emergency department with acute illness. Outpatient FBS and 2-h OGTT were performed after recovery from the acute illness, resulting in diagnostic categorizations of prediabetes, diabetes, and dysglycemia (prediabetes or diabetes). Optimal cutoffs were determined and performance data identified for cut points.

RESULTS

A total of 618 patients were included, with a mean age of 49.7 (±14.9) years and mean HbA_1c of 5.68% (±0.86). On the basis of an OGTT, the prevalence of previously undiagnosed prediabetes and diabetes was 31.9 and 10.5%, respectively. The optimal HbA_1c-screening cutoff for prediabetes was 5.7% (area under the curve AUC] = 0.659, sensitivity = 55%, and specificity = 71%), for dysglycemia 5.8% (AUC = 0.717, sensitivity = 57%, and specificity = 79%), and for diabetes 6.0% (AUC = 0.868, sensitivity = 77%, and specificity = 87%).

CONCLUSIONS

We identified HbA_1c cut points to screen for prediabetes and diabetes in an emergency department adult population. The values coincide with published outpatient study findings and suggest that an emergency department visit provides an opportunity for HbA_1c-based dysglycemia screening.There are 26.8 million people with diabetes in the U.S., and by the year 2030, it is estimated to increase to 36 million people (1). Current estimates are that 27% of individuals with diabetes remain undiagnosed, and by the time of diagnosis, there often are microvascular and macrovascular abnormalities found (2–4). Early recognition is important because lifestyle modifications and medications can reduce the incidence of diabetes in people at high risk (5), and the treatment of diabetes can prevent or delay microvascular end-organ complications.The use of hemoglobin A_1c (HbA_1c) to diagnose prediabetes and diabetes recently was recommended by the American Diabetes Association (ADA) (6). HbA_1c testing has an advantage over glucose-based testing because it does not require fasting, and the test can be performed at any time. Guidelines recommend an HbA_1c ≥6.5% to diagnose diabetes and HbA_1c between 5.7 and 6.4% for identifying prediabetes. These cutoff values for HbA_1c are derived in part from outpatient studies and are based on populations of those not acutely ill at the time of testing (7–9).Less attention has been given to screening and diagnosing diabetes and prediabetes in acute-care settings such as the emergency department, where blood is routinely drawn to manage acute illness and clinicians are available to interpret the results. The HbA_1c test can be quickly performed in many different clinical settings, including the hospital. However, it is not known whether HbA_1c thresholds differ between the higher-risk acute-care and the general outpatient populations. The purpose of this study was to determine optimal HbA_1c-screening cutoff points for undiagnosed dysglycemia in the emergency department setting using follow-up fasting blood glucose (FBS) and 2-h oral glucose tolerance tests (OGTTs) as the criterion gold standard.