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297 HEMOGLOBIN N-BALTIMORE: ANOTHER CAUSE OF FALSE HEMOGLOBIN A1C ESTIMATION.
  1. E. A. Nyenwe1,
  2. S. V. Batakke1,
  3. E. A. Mack1,
  4. J. N. Fisher1
  1. 1Division of Endocrinology, University of Tennessee Health Science Center, Memphis, TN

Abstract

Estimation of glycohemoglobin (HbA1c) has become a very useful tool in the management of patients with diabetes. It provides an index of long-term glycemic control, which correlates with the development of chronic complications of diabetes. Over 150,000 patients with diabetes are estimated to have hemoglobin (Hb) variants in the United States, but this number may be as high as one-third of all diabetic patients in some parts of the world. Most of the hemoglobinopathies are clinically silent, but some of them may cause biochemical aberrations, which can interfere with assays for HbA1c. Some Hb variants, such as HbS, HbC, and HbF, are known to affect glycohemoglobin assays, but Hb N-Baltimore has not been reported to give false HbA1c estimation. We present a 28-year-old African American woman with a history of diabetes whose diagnosis was based on one abnormal blood glucose level of 180 mg/dL and elevated HbA1c of 8.6%. She was managed on oral antidiabetic agents, but her HbA1c remained elevated despite consistently normal or low blood glucose levels. Repeat HbA1c estimation in another laboratory was not possible because of detected interference with the assay from possible abnormal Hb. Plasma frutosamine level was reported as normal. Hb electrophoresis revealed Hb N-Baltimore. The patient subsequently discontinued all antidiabetic agents and remained in good glycemic control. This case documents Hb N-Baltimore as a cause of false HbA1c measurement in clinical medicine. The implication of this phenomenon in patients with diabetes is obvious. It underscores the need to use blood glucose levels rather than HbA1c estimation in the diagnosis of diabetes. Second, when there is disparity between blood glucose measurement and HbA1c estimation, an alternative to glycohemoglobin measurement, such as frutosamine, should be considered for the monitoring of long-term glycemic control. Hb electrophoresis should also be done to confirm or exclude an Hb variant as the etiology of a false HbA1c result. Lastly this case demonstrates that clinicians should be aware of the method for estimating HbA1c in their institutions and how this could be affected by the Hb variants. Interaction between clinicians and laboratory personnel is to be encouraged as this would be helpful in the management of cases such as the one presented here.

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