Most blood glucose tests show how much glucose is in the blood at a particular point in time. The hemoglobin A1C test gives a more long-term view of blood sugar levels.
Glucose molecules attach to hemoglobin in the blood. This is the protein in red blood cells that colors the blood. Hemoglobin also transports oxygen and carbon dioxide. Glucose molecules attach to only a fraction of your red blood cells. However, this occurs more readily when there is more glucose in the blood. The attachment lasts for many weeks and as long as three months.
Hemoglobin proteins that have bound glucose in this way are called A1C proteins, or glycohemoglobin. They can be identified by a blood test. This test tells you the percentage of your hemoglobin proteins that are in the A1C form. It can give an overall picture of your blood glucose control in the prior couple of months. The higher your A1C percentage, the higher your average blood sugar level has been.
Measurement of A1C provides a broad view of blood glucose control. It is not skewed by a single meal or by a day or two of missed medicine doses or irresponsible eating. Conversely, it is not changed by a day or two of very responsible eating. It gives the big picture, as opposed to the narrow snapshot of a blood glucose reading.
The A1C level reflects a glucose average that roughly corresponds to the numbers in the following table.
No fasting is necessary for an A1C test. Blood is taken from a vein and analyzed in a laboratory. As an alternative, you also can buy a home A1C monitor that can test a finger-prick sample of blood. People without diabetes usually have an A1C value below 6%.
Your doctor will discuss with you the result of your test and what it means for diabetes management. If your hemoglobin A1C is above normal, you may need a change in your diet and/or medicines. Most doctors test hemoglobin A1C in people with diabetes two to four times a year. However, if you are having trouble controlling your levels, the test may be done more often.
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