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A1C test is a blood test used to diagnose diabetes and monitor the progress of a treatment plan. The test result reflects the average blood sugar levels in the past 3 months.
A1C is a type of glycated hemoglobin – a hemoglobin that is bound to glucose. Hemoglobin is the major protein of red blood cells. A1C forms as a result of interaction between red blood cells and sugar in the blood. The higher the blood glucose levels, the more glucose binds to hemoglobin, the greater the amount of A1C. The A1C blood test reports the percentage of hemoglobin that is bound to glucose.
Once a hemoglobin is glycated, it remains that way in the blood, until the red blood cell carrying it is removed from the circulation. Because the average lifespan of a red blood cell is 3 to 4 months, A1C measurement represents the status of blood glucose for the past 3 months or so.
A normal blood glucose level corresponds to an A1C result of less than 5.7%. An A1C level higher than 6.5% indicates diabetes. Between 5.7 and 6.5% is prediabetes.
An estimated average glucose level, eAG, measured in concentration units, milligrams per deciliter or millimoles per liter, can be calculated and often reported in addition to the A1C percentage. eAG helps patients link A1C to the numbers they obtain at home using a blood sugar measuring device.
A1C is an important tool for managing diabetes. For most diabetics, the goal is to bring A1C level down to 7% or less. However, patient’s age and other health conditions must be taken into account when setting goals. In general, younger patients who don’t often experience severe low glucose, known as hypoglycemia, need lower goals to avoid diabetes complications in the many years ahead. Older patients or those having frequent low-glucose episodes, may have a higher goal.
When A1C can NOT be used?
It is important to note that several factors can affect the accuracy of A1C test result, in which case, unless corrections can be made, A1C cannot be used to assess blood glucose levels. For example, people with blood disorders such as sickle cell disease, thalassemia, or hemolytic anemia may have a lower than expected A1C because their red blood cells have a shorter lifespan. Iron deficiency anemia, on the other hand, is associated with increased red blood cell lifespan and falsely high A1C measurements. Some people of African, Mediterranean, or Southeast Asian descent may have uncommon forms of hemoglobin that produce falsely high or low results. Certain kidney and liver diseases may affect the turnover rate of red blood cells and give rise to inaccurate A1C readings. Finally, recent blood loss or transfusion will also skew the test results.
