Читать книгу Diabetes For Dummies - Рубин Алан Л. - Страница 10

Your blood glucose level is the level of sugar in your blood, a key measure of diabetes. Individual blood glucose tests are great for deciding how you’re doing at that moment and what to do to make it better, but they do not give the big picture. They are just a moment in time. Glucose can change a great deal even in 30 minutes. What you need is a test that gives an integrated picture of many days, weeks, or even months of blood glucose levels. The test that accomplishes this important task is called the hemoglobin A1c.

Hemoglobin is a protein that carries oxygen around the body and drops it off wherever it’s needed to help in all the chemical reactions that are constantly taking place. The hemoglobin is packaged within red blood cells that live in the bloodstream for 60 to 90 days. As the blood circulates, glucose in the blood attaches to the hemoglobin and stays attached. It attaches in several different ways to the hemoglobin, and the total of all the hemoglobin attached to glucose is called glycohemoglobin. Glycohemoglobin normally makes up about 6 percent of the hemoglobin in the blood. The largest fraction, two-thirds of the glycohemoglobin, is in the form called hemoglobin A1c, making it easiest to measure. The rest of the hemoglobin is made up of hemoglobin A1a and A1b.

The more glucose in the blood, the more glycohemoglobins form. Because red blood cells carrying glycohemoglobin remain in the blood for two to three months, glycohemoglobin is a reflection of the glucose control over the entire time period and not just the second that a single glucose test reflects.

Hemoglobin A1c has a number of advantages over the variety of glucose tests for diagnosing diabetes, which I discuss in the later section “Diagnosing diabetes through testing.” Hemoglobin A1c is now as well standardized as glucose testing, and it has the following benefits:

✔ A1c reflects chronic high blood glucose rather than a few seconds in time.

✔ A1c has been found to reflect future complications (see Chapter 5) better than fasting glucose.

✔ Fasting isn’t necessary, and acute changes like diet and exercise don’t affect A1c.

✔ A1c is not as affected by sample delays on the way to or in the lab.

✔ A1c is also used to follow the course of diabetes, so the level of treatment needed is immediately understood.

✔ A1c is cost-effective, because no further testing is immediately necessary when results are abnormal (whereas an abnormal glucose test requires another glucose or A1c as the next test).

Following are some disadvantages of hemoglobin A1c:

✔ Abnormal glucose after eating is a better predictor of heart disease than A1c.

✔ Some subjects with anemia, a recent blood transfusion, and abnormal hemoglobin types (there are several types of hemoglobin) produce an unreliable A1c result.

✔ Different ethnic groups have different levels for their abnormal A1c.

According to one study, in the United States, hemoglobin A1c detects that diabetes is present in one in every five people admitted to a hospital for any reason without a diagnosis of diabetes.