Testing Blood Sugar with Sickle Cell Anemia

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Testing Blood Sugar with Sickle Cell Anemia

Question:

I am a type 2 diabetic with sickle-cell trait. Why does my endocrinologist recommend that I take a fructosamine test rather than the standard A1C to test my blood sugar? Are A1C results less reliable in someone carrying the sickle-cell trait?

Answer:

Sickle cell anemia is one medical condition that can potentially cause a falsely low A1C test.

The A1C test estimates how well blood sugar (glucose) has been controlled. When glucose is high, some attaches to the hemoglobin in red blood cells and stays chemically "stuck" there. If glucose is repeatedly high, a high percentage of your hemoglobin will have a "sugared" appearance. The hemoglobin is then called "hemoglobin A1C."

Newly made red blood cells have hemoglobin that has not been changed to the A1C form. Your body recycles red blood cells and hemoglobin every 120 days or so. One by one, the "sugared" hemoglobin is removed from your bloodstream. If this recycling process is sped up, your A1C test result would look lower.

Sickle cell anemia can cause cells to be recycled faster, and this could cause a falsely low A1C test. Also, depending on the brand of test used, sickle cell anemia can make it harder for some labs to measure A1C accurately.

The fructosamine test is similar to the A1C test, but instead of measuring sugar changes on your hemoglobin, it measures sugar changes on your albumin protein. Albumin protein is cleared out of the blood regularly, just like hemoglobin. However, it is not affected by the pattern of red blood cell break-down and recycling, nor by genetic variations in your hemoglobin type.

Mary Pickett, M.D., is a lecturer for Harvard Medical School and an assistant professor of medicine at Oregon Health & Science University in Portland, OR. At OHSU, she practices general internal medicine and teaches medical residents and students.

Last updated:	July 20, 2009