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Diabetes Care 27:2570, 2004
© 2004 by the American Diabetes Association, Inc.

Letters: Comments and Responses

Biological Variation in HbA1c Predicts Risk of Retinopathy and Nephropathy in Type 1 Diabetes

Response to Twomey et al.

Stuart A. Chalew, MD1, Robert J. McCarter, SCD2 and James M. Hempe, PHD3

1 Department of Endocrinology, Children’s Hospital, New Orleans, Louisiana
2 Department of Bioinforatics and Statistics, Children’s National Medical Center, Washington, D.C
3 Department of Pediatrics, Louisiana State University Health Sciences Center, New Orleans, Louisiana

Address correspondence to Stuart A. Chalew, MD, Children’s Hospital, Department of Endocrinology, 200 Henry Clay Ave., New Orleans, LA 70118. E-mail: schale{at}lsuhsc.edu

We appreciate the comments of Twomey et.al. (1) in regard to our recent article (2) about biological variation in HbA1c and its relationship to microvascular complications. They point out potential obstacles to the general use of the hemoglobin glycation index (HGI) by clinical practitioners. The best approach to calculating the HGI of individual patients from populations besides the Diabetes Control and Complications Trial (2) and our original patient data (3) still needs to be established for the clinician.

We point out, however, that a moving average of an individual patient’s HbA1c will not provide the same information as the HGI. Our analyses indicate that HbA1c carries two important components of clinically relevant information: 1) an estimate of the patient’s preceding mean blood glucose (MBG) and 2) patient-specific factors besides MBG that influence glycation of hemoglobin. Both of these components are independently associated with the risk of development of microvascular complications (2). Currently, clinical therapy is only directed at altering the first component. Calculation of the HGI allows us to separate the two components of risk from the patient’s HbA1c measurements. In this fashion, individual patients who have consistently high or low hemoglobin glycation statuscan be identified. However, calculating a patient’s HGI requires knowledge of the patient’s preceding MBG, the population relationship between HbA1c and MBG, and the patient’s HbA1c.

We foresee the future development of databases that will assist clinicians in calculating an HGI necessary to assess the hemoglobin glycation status of their patients. These computational sources will need to be referenced to population data that are specific for the methods of determining both the MBG and HbA1c used for that particular patient.

References

  1. Twomey PJ, Viljoen A, Reynolds TM, Wierzbicki AS: Biological variation in HbA1c predicts risk of retinopathy and nephropathy in type 1 diabetes (Letter). Diabetes Care 27:2569–2570, 2004[Free Full Text]
  2. McCarter RJ, Hempe JM, Gomez R, Chalew SA: Biological variation in HbA1c predicts risk of retinopathy and nephropathy in type 1 diabetes. Diabetes Care 27:1259–1264, 2004[Abstract/Free Full Text]
  3. Hempe J, Gomez R, McCarter R, Chalew S: High and low hemoglobin glycation phenotypes in type 1 diabetes: a challenge for interpretation of glycemic control. J Diabetes Complications 16:313–320, 2002[Medline]

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