Do not rely on HbA1c measurement alone

A 70-year-old Palestinian woman was referred because her primary care physician appropriately felt that she needed better control of her type 2 diabetes. Her HbA1c was 8%, corresponding to an average whole blood glucose of 182.

Review of other lab studies drawn that same day suggested that her glycemic control might be even worse than initially thought. Her hemoglobin was 9.6, mean red cell volume 77, and red blood cell distribution width was elevated at 17.6. Given her Middle Eastern background, it is likely this patient had thalassemia, but whatever the cause, increased red blood cell turnover will often give a falsely low indication of the degree of glycation and there is some suggestion that there is also direct inteference with some of the HbA1c assays.

Conversely, states of low red cell turnover, such as chronic kidney disease stage 4 and 5, can give false assurance that the diabetes is well controlled.

While HbA1c is a good measure of control of diabetes it should not be the only measure relied upon. Patients should be encouraged to bring in a record of their CBG—either hand-written or stored on their blood glucose meter. Many of these meters can now be downloaded to a PC or laptop and graphical information about CBG fluctuations can be very informative to the patient and physician. Of course, this only works if the patient remembers to check CBG as directed.