The Relationship of Plasma Glucose and HbA1c Levels among Emergency Department Patients with No Prior History of Diabetes Mellitus

Abstract

Patients without a history of diabetes mellitus may be incidentally found to be hyperglycemic in the emergency department (ED). If the hyperglycemia is due to undiagnosed diabetes, then an opportunity for detection exists. Hemoglobin A1c (HbA1c) provides a weighted average of blood glucose levels over the past several months; high HbA1c levels could indicate diabetes. The objective of this study was to determine whether hyperglycemia in ED patients without a history of diabetes was associated with higher HbA1c levels. This was a prospective nonconsecutive case series of adults aged 18 years or older presenting to the ED with acute illness for whom a plasma glucose sample was drawn for clinical management. A history of diabetes/hyperglycemia or current symptoms of diabetes excluded patients. HbA1c levels were analyzed for a glucose cutoff of 110 mg/dL; the data were further analyzed using additional glucose cutoffs. Based on the Third National Health and Nutrition Examination Survey outpatient screening data, an HbA1c level > or =6.2% was considered elevated (sensitivity of 63% and specificity of 97% for identifying diabetes). There were 541 patients enrolled; the glucose level correlated with the HbA1c level (r = 0.60, p < 0.001). Among the 331 patients with a glucose level > or =110 mg/dL, 22.4% had an elevated HbA(1c) level; among the 210 patients with a glucose level < 110 mg/dL, 7.6% had an elevated HbA1c level. There were few patients (n = 13) with a glucose level > or =200 mg/dL, but most (85%) had an elevated HbA1c level. Among the 140 patients with a mildly elevated glucose level (110-125 mg/dL), 16.4% had an elevated HbA(1c) level. Elevated HbA1c levels are found in ED patients with elevated random plasma glucose values. ED patients with hyperglycemia may warrant referral for diabetes testing.