|What is prediabetes?
Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are two conditions you might have before you are diagnosed with type 2 diabetes. Both conditions are called prediabetes.
People whose blood glucose levels are higher than normal but not high enough to qualify as diabetes can be diagnosed with either impaired fasting glucose or impaired glucose tolerance. Prediabetes is diagnosed in individuals who have an A1C of 6.0% to 6.4%. People with IFG or IGT are at a higher risk of developing diabetes. They are also at a higher risk of developing heart disease.
It is important to know about IFG and IGT in order to prevent or delay the actual development of diabetes. In one study called the Diabetes Prevention Program (see below), about 11% of people with prediabetes developed type 2 diabetes each year during the 3-year follow-up period. Other studies show that most people with prediabetes develop type 2 diabetes within 10 years.
How Does This Information Help You If You Already Have Diabetes?
If you already have diabetes, this information may not be particularly helpful to you personally. But it may help a family member. As you know, family members of someone with diabetes have a higher risk of developing diabetes than people who do not have relatives with diabetes. Thus, family members who know they have IFG or IGT may be able to take the necessary steps to prevent diabetes from developing.
Know Your Risks for Developing Diabetes
If you do not have diabetes, you will not know you have prediabetes. There are no symptoms. However, you may want to be tested for IFG and IGT.
The Canadian Diabetes Association recommends that people older than 40 years of age be tested for IFG or IGT. The association strongly recommends that people older than 40 years of age who are also overweight be tested. "Overweight" means having a body mass index (BMI) of 25 kg/m2 or more. Asian Americans with a BMI of 23 kg/m2 or more should consider being tested.
In addition, people who are younger than 45 and are overweight should be tested if they have another risk factors, such as:
- A family history of diabetes
- Physical inactivity
- African American, Native American, or Pacific Island ethnic background
- High blood pressure
- A history of low HDL and high LDL cholesterol levels
- A history of gestational diabetes or giving birth to a baby who weighed more than 9 pounds
- A history of polycystic ovarian syndrome
How Will You Know If You Have Prediabetes?
Blood tests can determine if you have prediabetes (impaired fasting glucose or impaired glucose tolerance).
Testing for Impaired Fasting Glucose
When your healthcare provider orders blood tests during your routine yearly checkup, the fasting blood glucose test is usually included to see if you have impaired fasting glucose.
After a fast of 8 to 12 hours, your blood is drawn to measure the blood glucose level.
A blood glucose level measuring below 6 mmol/L (100 mg/dL) is normal. If your blood glucose level is between 6.0 and 6.9 mmol/L (100 mg/dL and 125 mg/dL), you have prediabetes (impaired fasting glucose). If your blood glucose level is 7 mmol/L (126 mg/dL) or more, you have diabetes. This test needs to be repeated on another day to confirm the diagnosis.
Testing for Impaired Glucose Tolerance
The test used to diagnose impaired glucose tolerance is called an oral glucose tolerance test (OGTT). It is not a routine test. The oral glucose tolerance test detects elevated glucose levels before and after you drink a measured amount of glucose (a type of carbohydrate).
Before the test, you must fast overnight (at least 8 hours but not more than 16 hours), and go to your healthcare provider's office or the laboratory in the morning. The morning of the test, you should not smoke or drink coffee. During the test, which lasts 2 hours, you will be asked to sit in a waiting area and not to smoke or eat. Walking more than a small distance, eating, and smoking can interfere with getting accurate test results.
This is what you can expect to happen during the test
A blood sample is drawn to determine your fasting blood glucose level. After this, you will drink 75 grams of a glucose solution in the form of a very sweet-tasting beverage. (If you are pregnant, you will receive 100 grams of glucose. The dosage for children is based on body weight.) Blood samples are taken at regular intervals for 2 hours after you drink the liquid to measure your blood glucose level.
This is what the results of the OGTT mean: A blood glucose level measuring below 7.8 mmol/L (140 mg/dL) 2 hours after drinking the glucose solution is normal. If your blood glucose level is between 7.8 and 11 mmol/L (140 mg/dL and 199 mg/dL) 2 hours after drinking the glucose solution, you have prediabetes (impaired glucose tolerance). If your blood glucose level is 11.1 mmol/L (200 mg/dL) or more 2 hours after drinking the glucose solution, you have diabetes. This test needs to be repeated on another day to confirm the diagnosis.
Impaired glucose tolerance is the first stage of not having enough insulin. It is characterized by a reduced amount of insulin secretion right after eating or drinking something with carbohydrates; in this case, glucose.
The role of insulin (a hormone secreted by the pancreas) is to move glucose from the blood into cells to supply energy. Having IGT means that your body is unable to efficiently process the glucose you drank during the test. In your daily life, this means that your blood glucose is likely to be high after meals.
Which Test Is Better?
Both tests have advantages:The fasting blood glucose test is easier and less expensive to administer than the OGTT. This test, therefore, is used moreoften by healthcare providers. However, the OGTT can identify prediabetes earlier in the disease process than the fasting blood glucose test.
If You Have Prediabetes, Can You Slow the Progression to Diabetes?
Diabetes is a progressive disease. If you are told you have prediabetes (impaired fasting glucose or impaired glucose tolerance), you are being given a heads-up that you may be progressing to diabetes. You can then take steps to prevent or delay the progression.
You may also be able to delay the worsening of diabetes, depending on how early you are diagnosed. Researchers estimate that there may be as many as 5 million people who do not know they have diabetes because they have not yet been diagnosed. Most people diagnosed with diabetes have had elevated blood glucose levels that have gone undetected and have been doing damage for 4 to 7 years.
Lifestyle Changes Help
Two studies have shown that it is possible to prevent the progression of prediabetes to diabetes with two small lifestyle changes:
- Physical activity: 30 minutes per day of walking or other moderate-intensity exercise
- Weight loss: 5% to 7% of body weight
Finnish Diabetes Prevention Study
In June 2000, the results of the Finnish Diabetes Prevention Study were presented at the American Diabetes Association annual meeting. Researchers studied more than 500 adults whose average age was 55 who had been diagnosed with impaired glucose tolerance. Their glucose levels were higher than normal but not high enough to qualify as diabetes. All participants were overweight.
About half of the participants were randomly assigned to an intervention group. People in this group met several times a year with a dietitian who provided personalized advice on weight reduction; intake of calories, carbohydrates and fats; and exercise.
The other participants were assigned to a no-intervention group. People in this group also met with a dietitian and received personalized advice, but they met only once a year.
After 4 years, people in the intervention group, who received frequent and consistent education and support, achieved an average weight loss of 7.7 pounds compared with only 1.8 pounds in the no-intervention group. Of the 500 participants in the study, 83 developed diabetes. Only one third (26) of those who developed diabetes were members of the intervention group.
So, a weight loss of less than 8 pounds made a significant difference in the rate that people with impaired glucose tolerance developed diabetes. These results prompted the study coordinator to state, "Based on this evidence, such individualized intervention programs should become part of standard medical practice and be covered by health insurance for people at high risk for diabetes."
Diabetes Prevention Program
In August 2001, the National Institute of Diabetes and Digestive and Kidney Diseases released the results of the Diabetes Prevention Program. This major clinical trial compared diet and exercise to treatment with the oral diabetes medication metformin (Glucophage) in 3,234 people with impaired glucose tolerance. Results from the study clearly showed that a weight loss of as little as 5% to 7% and 30 minutes a day of walking can reduce the risk of getting type 2 diabetes by 58%. The diabetes medication metformin also reduced the risk of developing diabetes in people with IGT, but to a lesser extent (31%) than with lifestyle changes.
Devising a Course of Treatment
Know your fasting blood glucose levels. If your numbers are higher than normal, but not high enough to be diagnosed as diabetes, take it seriously. Initiate lifestyle strategies to prevent or delay the progression to diabetes. If you suspect you may have prediabetes, ask your healthcare provider to perform a 2-hour glucose tolerance test.
Diabetes Prevention Program Research Group. Diabetes Prevention Program: design and methods for a clinical trial in the prevention of type 2 diabetes. Diabetes Care. 1999;22:623-634.
Diabetes Prevention Program Research Group. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. New England Journal of Medicine. 2002;346(6):393-403.
Diet and exercise dramatically delay type 2 diabetes: diabetes medication metformin also effective. National Institute of Diabetes and Digestive and Kidney Diseases. Available at: http://www.niddk.nih.gov/welcome/releases/8_8_01.htm. Accessed March 8, 2004.
Ford EW, Giles WH, Dietz WH. Prevalence of the metabolic syndrome among US adults: findings from the third national health and nutrition examination survey. JAMA (Journal of the American Medication Association). 2002;287:356-359.
How to tell if you have pre-diabetes. All About Diabetes. American Diabetes Association. Available at: http://www.diabetes.org/pre-diabetes/pre-diabetes-symptoms.jsp. Accessed March 17, 2004.
Pan X, Li G, Hu Y, et al. Effects of diet and exercise in preventing NIDDM in people with impaired glucose tolerance: the Da Qing IGT and diabetes study. Diabetes Care. 1997;20:537-544.
Prevention or delay of type 2 diabetes. American Diabetes Association. Diabetes Care. 2003:26(suppl 1);S62-S69. Available at: http://care.diabetesjournals.org/cgi/content/full/26/suppl_1/s62. Accessed March 8, 2004.
Richard J-L, Sultan A, Daures JP, et al. Diagnosis of diabetes mellitus and intermediate glucose abnormalities in obese patients based on ADA (1997) and WHO (1985) criteria. Diabetic Medicine. 2002:19(4)292-299.
Screening for diabetes. American Diabetes Association. Diabetes Care. 2002;25:21-24. Available at: http://care.diabetesjournals.org/cgi/content/full/25/suppl_1/s21. Accessed March 8, 2004.
Standards of medical care for patients with diabetes mellitus. American Diabetes Association. Diabetes Care. 2002;25:33-49. Available at: http://care.diabetesjournals.org/cgi/content/full/25/suppl_1/s33. Accessed March 8, 2004.
Tuomilehto J, Lindstrom J, Eriksson JG, et al, for the Finnish Diabetes Prevention Study Group. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. New England Journal of Medicine. 2001;344:1343-1350