Diabetes Mellitus (cont.)
Melissa Conrad Stöppler, MD
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
In this Article
- Diabetes facts
- What is diabetes?
- How many people in the US have diabetes?
- 6 early signs and symptoms of diabetes
- How do I know if I have diabetes?
- What causes diabetes?
- What are the different types of diabetes?
- Type 1 diabetes
- Type 2 diabetes
- What are the other types of diabetes?
- How is diabetes diagnosed?
- Why is blood sugar checked at home?
- What are the acute complications of diabetes?
- What are the chronic complications of diabetes?
- What can be done to slow the complications of diabetes?
- Type 2 Diabetes - Slideshow
- Diabetes and Foot Problems - Slideshow
- Take the Diabetes Quiz!
- Diabetes FAQs
- Find a local Endocrinologist in your town
How is diabetes diagnosed?
The fasting blood glucose (sugar) test is the preferred way to diagnose diabetes. It is easy to perform and convenient. After the person has fasted overnight (at least 8 hours), a single sample of blood is drawn and sent to the laboratory for analysis. This can also be done accurately in a doctor's office using a glucose meter.
- Normal fasting plasma glucose levels are less than 100 milligrams per deciliter (mg/dl).
- Fasting plasma glucose levels of more than 126 mg/dl on two or more tests on different days indicate diabetes.
- A random blood glucose test can also be used to diagnose diabetes. A blood glucose level of 200 mg/dl or higher indicates diabetes.
When fasting blood glucose stays above 100mg/dl, but in the range of 100-126mg/dl, this is known as impaired fasting glucose (IFG). While patients with IFG or prediabetes do not have the diagnosis of diabetes, this condition carries with it its own risks and concerns, and is addressed elsewhere.
The oral glucose tolerance test
Though not routinely used any longer, the oral glucose tolerance test (OGTT) is a gold standard for making the diagnosis of type 2 diabetes. It is still commonly used for diagnosing gestational diabetes and in conditions of pre-diabetes, such as polycystic ovary syndrome. With an oral glucose tolerance test, the person fasts overnight (at least eight but not more than 16 hours). Then first, the fasting plasma glucose is tested. After this test, the person receives an oral dose (75 grams) of glucose. There are several methods employed by obstetricians to do this test, but the one described here is standard. Usually, the glucose is in a sweet-tasting liquid that the person drinks. Blood samples are taken at specific intervals to measure the blood glucose.
For the test to give reliable results:
- The person must be in good health (not have any other illnesses, not even a cold).
- The person should be normally active (not lying down, for example, as an inpatient in a hospital), and
- The person should not be taking medicines that could affect the blood glucose.
- The morning of the test, the person should not smoke or drink coffee.
The classic oral glucose tolerance test measures blood glucose levels five times over a period of three hours. Some physicians simply get a baseline blood sample followed by a sample two hours after drinking the glucose solution. In a person without diabetes, the glucose levels rise and then fall quickly. In someone with diabetes, glucose levels rise higher than normal and fail to come back down as fast.
People with glucose levels between normal and diabetic have impaired glucose tolerance (IGT) or insulin resistance. People with impaired glucose tolerance do not have diabetes, but are at high risk for progressing to diabetes. Each year, 1% to 5% of people whose test results show impaired glucose tolerance actually eventually develop diabetes. Weight loss and exercise may help people with impaired glucose tolerance return their glucose levels to normal. In addition, some physicians advocate the use of medications, such as metformin (Glucophage), to help prevent/delay the onset of overt diabetes.
Research has shown that impaired glucose tolerance itself may be a risk factor for the development of heart disease. In the medical community, most physicians now understand that impaired glucose tolerance is not simply a precursor of diabetes, but is its own clinical disease entity that requires treatment and monitoring.
Evaluating the results of the oral glucose tolerance test
Glucose tolerance tests may lead to one of the following diagnoses:
- Normal response: A person is said to have a normal response when the 2-hour glucose level is less than 140 mg/dl, and all values between 0 and 2 hours are less than 200 mg/dl.
- Impaired glucose tolerance (prediabetes): A person is said to have impaired glucose tolerance when the fasting plasma glucose is less than 126 mg/dl and the 2-hour glucose level is between 140 and 199 mg/dl.
- Diabetes: A person has diabetes when two diagnostic tests done on different days show that the blood glucose level is high.
- Gestational diabetes: A pregnant woman has gestational diabetes when she has any two of the following:, a fasting plasma glucose of 92 mg/dl or more, a 1-hour glucose level of 180 mg/dl or more, or a 2-hour glucose level of 153 mg/dl, or more.
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