Thursday, May 31, 2012

Hemoglobin Variants and A1c Tests

What's your A1c? It's a question I've heard many times from people in the DOC. The A1c is a blood test that shows how much glucose has been circulating in our blood for the past three months.

Technically speaking...

The A1C test measures the amount of glycated hemoglobin in the blood, which indicates average blood glucose levels over the preceding 2 to 3 months. Also called glycated hemoglobin or glycohemoglobin, the A1C test is based on the addition of glucose to hemoglobin over the typical 120-day life span of a red blood cell. Formation of glycated proteins is proportional to the concentration of glucose in the blood. The A1C test helps gauge risk of long-term complications; studies have demonstrated substantial reductions in long-term complications of diabetes with lowering of A1C. --- National Diabetes Information Clearinghouse

Obviously the A1c is a valuable test. Unfortunately I have never had a valid one. My doctors have tried getting my A1c, but the answers are always wrong, because I have a hemoglobin variant.

 Approximately 7% of the world's population carries a hemoglobin (Hb) variant. In the United States the most common variant is called HbAS. It is a genetic marker for a disease called sickle cell anemia. I do not have sickle cell disease, but I do carry the gene or trait. If I married someone who also had the gene for sickle cell anemia we would have a 1 in 4 chance of passing on the disease to our child.

For the most part, having HbAS is no big deal. Except for one thing: HbA1c testing doesn't work because I don't have Hb hemoglobin. My red blood cells don't live 120 days. "Studies that have measured Hb S RBC survival... demonstrating that the lifespan of RBCs in Hb S trait is approximately 93 days compared to 120 days in hematologically normal persons." Since my red blood cells only live 93 days, and the test assumes they live 120 days, a standard A1c test is inaccurate.

About one in 12 African Americans has sickle cell trait. About one in 100 Hispanic Americans/Latinos has sickle cell
trait. It and other hemoglobin variants are distributed throughout the world. If you have the gene for sickle cell anemia, or know you have any kind of hemoglobin variant, please inform your doctor. Your A1c test results may be invalid. You may not be getting the right treatment for your diabetes.

My medical team are trying to figure out how to accurately measure my A1c. When they figure out how, I'll let you know.

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