October 1, 2013
Inaccurate Results from the A1c Test - Causes
Below is a simple graphic image of a red blood cell. One of the functions of the red blood cells is to carry oxygen to all the cells in the body. Hemoglobin within the red blood cells is the part that carries this oxygen. A vital part of the hemoglobin molecule is a fraction called hemoglobin A.
Glycosylation is the process of glucose binding to the hemoglobin areas of the red blood cells. Elevated blood glucose levels means more glycosylation happens.
A small, but measurable part of the hemoglobin A labeled A1 is formed when A is glycosylated. A further fraction of the A1 known as the hemoglobin A1c can also be measured. This A1c fraction is the area used for measuring the effective level of blood glucose management.
Red blood cells typically live for about 120 days, after which they die and are removed from circulation. New red blood cells are produced to replace those taken out of circulation. Therefore, at any given time, there are red blood cells that have just been born and those that are about to die. The average age for all the red blood cells present in the human body at a given time is about 2 months old, or half the total lifespan. Glycosylation occurs continually throughout the life span of the red blood cell. The amount of glycosylation of the hemoglobin depends on the level of blood glucose in the body, the higher the blood glucose level, the more glycosylation will occur.
Because the average age of the total pool of red blood cells is 2 months, the A1C measured represents predominantly, but not totally, the level of management during the previous 2-month period. This means that the higher the result of the A1c level, the poorer the diabetes management was during the preceding two months. Since the Joslin Diabetes Center follows the ADA guidelines, I can only suggest that what they advise should be adjusted for your own goals. Joslin says for any A1c 7.0% or higher, the treatment regimen needs to be adjusted. This is from Joslin's Diabetes Deskbook, Chapter 2.
Despite how much is dependent on the A1c test, there are conditions that cause inaccurate results. They include people with:
#1. Sickle cell anemia
#2. Women in early stages of pregnancy because the fetus produces its own red blood cells
#3. Recently had blood transfusions, many red cells have not been present the entire time in the patient.
#4. Splenectomy, which causes red blood cells to live longer
#5. Anemias, because many of the red cells can average younger in age
There are a few other conditions, which can cause erroneous A1c's, but in general, these are rare. Even with the above A1c problems, the use of the test is still a powerful tool in the battle of diabetes management.
For another view on the value of A1c and using the home A1c kit, read this blog by David Mendosa.