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.
Getting a Wake-Up Call from Prediabetes
Diabetes doesn’t suddenly appear one day without previous notification from your body. For a period of time, which may last up to ten years, you may not quite achieve the criteria for a diagnosis of diabetes but not be quite normal either. During this time, you have what’s called prediabetes.
A person with prediabetes doesn’t usually develop eye disease, kidney disease, or nerve damage (all potential complications of diabetes, which I discuss in Chapter 5). However, a person with prediabetes has a much greater risk of developing heart disease and brain attacks than someone with entirely normal blood glucose levels. Prediabetes has a lot in common with insulin-resistance syndrome, also known as the metabolic syndrome, which I discuss in Chapter 5. The following two sections take the mystery out of whether you may have prediabetes by giving you some guidelines on when to get tested as well as explaining what testing for prediabetes involves.
Approximately 90 million people in the United States have prediabetes, although most of them don’t know it. Testing for prediabetes is a good idea for everyone over the age of 45. I also recommend getting tested if you’re under 45 and overweight or eat more than ten teaspoons of added sugar daily and have one or more of the following risk factors:
✔ A high-risk ethnic group: African American, Hispanic, Asian, or Native American
✔ High blood pressure
✔ Low HDL (“good” cholesterol)
✔ High triglycerides
✔ A family history of diabetes
✔ Diabetes during a pregnancy or giving birth to a baby weighing more than 9 pounds
Testing for prediabetes involves finding out your blood glucose level, the level of sugar in your blood. Prediabetes exists when the body’s blood glucose level is higher than normal but not high enough to meet the standard definition of diabetes mellitus (which I discuss in the section “Diagnosing diabetes through testing,” later in this chapter). Testing measures a random capillary blood glucose. If the level is greater than 100 milligrams per deciliter (mg/dl), a fasting plasma glucose or oral glucose tolerance test is performed. As of 2010, the American Diabetes Association recommends that the hemoglobin A1c (see the next section) can also be used for the definition. Table 2-1 shows the hemoglobin A1c and glucose levels that indicate prediabetes:
✔ If the glucose before the test (the fasting plasma glucose) is between 100 and 125 mg/dl, the person has impaired (abnormally high) fasting glucose, the glucose before eating (see Table 2-1). The glucose in the fasting state (no food for eight hours) is not normal, but it’s not high enough to diagnose diabetes.
✔ If the glucose is between 140 and 199 mg/dl at two hours after eating 75 grams of glucose, the person has impaired glucose tolerance. Both impaired fasting glucose and impaired glucose tolerance may be present.
✔ A hemoglobin A1c between 5.7 and 6.4 percent suggests prediabetes.
Table 2-1 Diagnosing Prediabetes
After a diagnosis of prediabetes is made, all the techniques described in Chapters 7 through 12 can help prevent the onset of clinical diabetes. If patients with prediabetes are left untreated, large numbers of these patients will develop diabetes over time. Preventing diabetes saves a person almost $13,700 in annual costs for the treatment of diabetes. And properly responding to a diagnosis of prediabetes prevented almost 20 percent of people with prediabetes from becoming diabetic.
Detecting Diabetes
When
