Hemoglobin A1c (Hb A1c) was measured for a 60-year-old woman with type 2 diabetes mellitus and hepatitis C (Hb A1c, 3.6%; reference interval, 4.3%–6.1%; Fig. 1). Her diabetes has been well controlled with metformin and low-dose glargine insulin, with Hb A1c values of 6.0%–7.1% and random glucose measurements of 115–235 mg/dL (6.4–13.0 mmol/L) [random glucose reference interval, <200 mg/dL (<11.1 mmol/L)]. She has been undergoing treatment with ribavirin, peginterferon alfa-2a, and erythropoietin. Her random plasma glucose concentration was 153 mg/dL (8.5 mmol/L), and her hemoglobin and hematocrit values were 12.1 g/dL (121 g/L) [reference interval, 11.2–15.7 g/dL (112–157 g/L)] and 38.9% (reference interval, 34.0%–45.0%), respectively.
What is the cause of the marked decline in Hb A1c?
What are the possible mechanisms for this decline?
Should the patient's diabetes regimen be adjusted on the basis of the Hb A1c result?
The answers are on the next page.
The marked decline in Hb A1c is caused by drug-induced anemia. Ribavirin can induce mild hemolysis (1, 2), decreasing the erythrocyte life span and hence decreasing the ability of hemoglobin to become glycated. Erythropoietin promotes erythrocytosis, and the greater proportion of new red blood cells could also lower the percentage of glycated hemoglobin (3). The patient's diabetes medications should not be adjusted on the basis of the Hb A1c value alone. Fructosamine measurement, multiple measurements of glucose throughout the day, or continuous glucose monitoring can be used.
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Authors' Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
- Received for publication August 18, 2011.
- Accepted for publication September 9, 2011.
- © 2012 The American Association for Clinical Chemistry