The hemoglobin A1c (A1c) test is a measure of blood sugar levels that is more reliable than the standard finger prick test performed at home, using a blood sugar meter. Hemoglobin is the major protein in red blood cells and carries oxygen throughout the body. If sugar levels are high in the blood, they will bind to hemoglobin. This forms glycated hemoglobin, which is detected by a hemoglobin A1c laboratory test. This reading provides a blood sugar measurement to help diagnose diabetes mellitus, or to help patients determine how well they are keeping their blood sugar under control.
Even when diabetic patients persistently monitor blood glucose levels at home using a blood sugar meter, there is quite a bit of variation in blood sugar levels. These levels often fluctuate throughout the day. It is difficult to get an accurate estimate of the overall blood sugar levels using this technique. The hemoglobin A1c test provides a reliable measure of blood sugar levels over the past three months, which is the approximate lifespan of a red blood cell.
Once sugar binds to the hemoglobin, it stays bound. Since it measures the amount of glycated hemoglobin in the red blood cells, the hemoglobin A1c test provides an estimate of blood sugar levels over the preceding months. A reading of between 4 to 6% is considered normal. Levels of 6.5 to 7% indicate a diagnosis of diabetes.
One might expect that low levels from a hemoglobin A1c test would be considered healthy for a diabetic, but this may not be the case. Diabetics struggle with high blood sugars, but low levels of blood sugars — hypoglycemia — can often be a problem as well. This is particularly true for Type 1 diabetics, who must inject insulin, or Type II diabetics on certain medications. Extreme levels of hypoglycemia can cause loss of consciousness and death. It is possible that low hemoglobin A1c test results indicate a mix of incidents of high blood glucose and hypoglycemia.
It is considered desirable for diabetics to have hemoglobin A1c levels below 6.5%. This correlates with a lowered degree of complications from diabetes, such as blindness, kidney problems, cardiovascular problems, gangrene, and loss of feeling in the feet. A patient should consult with his doctor to determine an ideal target range that will minimize high blood sugar levels, without causing hypoglycemia.
There are certain individuals for whom the hemoglobin A1c test is not recommended. People with certain types of anemia, such as hemolytic and sickle cell, degrade their blood cells. In other words, the red blood cells do not live a full three months. Also, people with Vitamin 12 or folic acid deficiency have blood cells that live much longer than normal. Individuals with these conditions are advised not to utilize this method of measuring their long-term blood sugar levels.
There is an alternate test to measure fructosamine levels, which is sometimes used instead of the hemoglobin A1c test, for patients who require it, such as those with hemolytic anemia. Unfortunately, it only measures blood sugar levels from the past two to three weeks. This test measures the reaction of glucose in the blood, with blood proteins, such as albumin. One such test is known as the glycated albumin test.