Along with blood glucose self-testing, the HbA1c test is an important measure of how effectively diabetes is being managed. While self-testing gives a reading of blood glucose at the moment the blood is drawn, which fluctuates throughout the day, the HbA1c test, performed in a laboratory, reveals the average blood glucose level over two to three months. Since the HbA1c glucose level is not affected by hour-by-hour fluctuations in glucose levels, such as meals, this reading is more of a "big picture" of glucose control.
What the test measures
The HbA1c test measures the amount of glucose adhered to haemoglobin in red blood cells. Haemoglobin is the part of the blood cell that carries oxygen. Glucose molecules in the bloodstream stick to haemoglobin and remain there for the life of the cell, about 120 days. Thus the test takes advantage of the life cycle of red blood cells and reveals an average glucose level going back two to three months. Results are expressed as "percents" that can be equated to the plasma blood glucose readings of day-to-day self-tests.
A non-diabetic's HbA1c glucose reading is 5 to 6 per cent. The goal in diabetes management is to reach a target hba1c result of 7 per cent or less-close to normal. It is important to keep in mind that the HbA1c can reflect the averaging of a period of high glucose levels with a period of low glucose levels, so this test alone is not sufficient evidence of glucose control.
According to the online resource Diabetes Chart, an HbA1c reading of 6.9 per cent equates to an average daily plasma blood glucose level of 168; 6.8 per cent equates to an average of 165; 6.7 per cent equates to an average of 161; 6.6 per cent equates to an average of 158; 6.5 per cent equates to an average of 154; 6.4 per cent equates to an average of 151; 6.3 per cent equates to an average of 147; 6.2 per cent equates to an average of 143; 6.1 per cent equates to an average of 140; 6.0 per cent equates to an average of 136; 5.5 per cent equates to an average of 118; 5.0 per cent equates to an average of 101; 4.5 per cent equates to an average of 83; and 4.0 per cent equates to an average of 65.
Conditions that skew reading
Chronic excessive alcohol use, kidney failure and high levels of triglycerides in the blood can cause falsely high HbA1c readings. Underproduction of haemoglobin, blood loss and sickle cell disease can cause falsely low HbA1c readings.
How often to be tested
If you are recently diagnosed with diabetes or your medications have been changed, your doctor will probably want an HbA1c test done every three months. If you have been hitting the target range with your HbA1c results, your doctor may ask for the test every six months.