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Preparing for your oral glucose tolerance test
If you have PCOS and you’re getting ready to have a glucose tolerance test, you may be wondering how to prepare for the test and what the results may mean. The test can help your doctor figure out whether you have a tendency toward diabetes and whether medications such as metformin might be helpful in treating the PCOS. The Oral Glucose Tolerance Test (OGTT) measures your body’s ability to use glucose.
What exactly is an Oral Glucose Tolerance Test (OGTT)?
What is Glucose?
What if my blood glucose level is high?
What do I need to do before my OGTT?
Do I need to eat anything special before the test?
What happens on the morning of the test?
At the Lab
When can I expect to get my test results?
What do the results mean?
What is the connection between impaired glucose tolerance (IGT) and PCOS?
Links/Resources
What exactly is an Oral Glucose Tolerance Test (OGTT)? 
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An OGTT is a way to measure your body’s ability to use glucose. Your pancreas (a gland located behind the stomach) makes a hormone called insulin, which helps your body use the glucose in your blood. If your pancreas does not make enough insulin or if your body is unable to use the insulin it makes, you may have a high blood glucose level. The test involves having your blood checked early in the morning and then drinking a special sugar beverage. After 2 hours you will have your blood tested again. Sometimes blood sugar levels are also drawn at other times such as one hour, three hours, or four hours after the glucose drink.
What is Glucose? top
Glucose is a type of sugar and the main source of energy used by your body. The glucose that your body uses for energy comes from many kinds of foods called carbohydrates, such as cereal, bread, rice, pasta, and other grains, not just sugary foods. Dairy products, fruits, and vegetables all contain carbohydrates as well. Your body uses the glucose it needs and then stores the rest as “glycogen” in your liver and muscles.
What if my blood glucose level is high? top
If the OGTT shows that your blood glucose levels are higher than normal, your doctor may tell you that you have “impaired glucose tolerance.” This often means that you are at risk for developing diabetes. Rarely, diabetes is diagnosed after an OGTT. Diabetes is a chronic (long term) illness that can happen when your body does not make enough insulin, or when your body has difficulty using the insulin that it does make.
What do I need to do before my OGTT? top
Your doctor will most likely give you either a glucose drink to take home or a prescription to bring to your pharmacy (for the special glucose drink). Some tests are done in a doctor’s office but most often the test is done in a lab at a hospital or clinic. The test takes several hours (most of it is waiting between blood tests) so you will need to clear your calendar for most of the morning of the test. If you need to fill a prescription, be sure to call your pharmacy ahead of time to check to see if they have the glucose drink in stock, as some pharmacies may not carry this item.
Do I need to eat anything special before the test? top
| 3 DAYS before the OGTT |
|---|
Plan on eating three healthy meals and snacks for 3 days before the test. You do not need to buy anything “special” but you do need to make sure you have healthy foods to eat. Your meals should be balanced with plenty of carbohydrates. Foods containing carbohydrates include:
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| 12 HOURS before the OGTT |
| DO NOT eat, smoke or do heavy exercise 12 hours before the test. (For example: If your test is scheduled for 8:00 AM - Do not eat, smoke or do heavy exercise after 8pm the night before). You may drink plain, NOT flavored water. |
What happens on the morning of the test? top
When you are ready to leave your home to have your test done, be sure to remember to bring:
- Your laboratory slips
- Your glucose drink
- A CD or MP3 player with head phones (to listen to music while you wait)
- Reading material/book/magazine
VERY IMPORTANT!!!!!!! DO NOT DRINK the glucose beverage until you arrive at the lab. The lab technician will tell you when to drink the glucose beverage.
At the Lab top
First: A fasting blood glucose test is done. This is a simple blood test that checks your blood sugar before you drink the glucose beverage.
Next: The lab technician will tell you to drink the glucose beverage. It will taste very sweet. It is important to drink the whole amount fairly quickly.
Waiting: After you finish drinking all of the glucose beverage, you will be asked to sit quietly until it is time (one to two hours) for your next blood test. You may read, listen to music, talk, or do another quiet activity while you’re waiting.
VERY IMPORTANT!!!!!!! DO NOT EAT or DRINK anything except plain water while you are waiting.
After the OGTT: Once your tests are done and the lab technician gives you permission to leave, you may go about your normal daily activities. You can go back to school or work, eat, drink, and do the regular exercise that you normally do.
When can I expect to get my test results? top
The lab will usually send your results to your doctor within a few days. You may already have a follow-up appointment scheduled or your doctor may call you to review your results and let you know if there are any concerns.
What do the results mean? top
The first test or “baseline” glucose test tells what your blood glucose level was before you drank the glucose beverage. Normal fasting blood glucose levels are less than 100 mg/dl (milligrams per deciliter). Your doctor may also check your insulin level.
The second result or your 2-hour blood glucose test measures your glucose two hours after you drank the glucose beverage. This level should be less than 140 mg/dl.
Normal levels of glucose mean that your body is able to use glucose the way it is supposed to. A high level of insulin means that your body does not use insulin well (even if your glucose levels are normal).
High levels of glucose mean that you have impaired glucose tolerance (IGT). This puts you at risk for developing diabetes.
What is the connection between impaired glucose tolerance (IGT) and PCOS? top
Doctors have known for some time that many of the symptoms of PCOS are caused by too much of the hormone testosterone. With PCOS, the ovaries make too much of this hormone which can result in extra facial and body hair and menstrual problems. Scientists now believe that many young women with PCOS also have high levels of insulin that can stimulate the ovaries to make testosterone. The high levels of insulin also increase the chance of getting diabetes. Your doctor will look at OGTT results along with other test results to figure out the best treatment for you including exercise, weight loss (if you are overweight), and sometimes taking medication.
Understanding how to prepare for an OGTT test and what the results mean can help you take charge of your PCOS. Making healthy food choices, exercising, and talking about your medication options with your doctor is the best way to keep your body healthy.
Links/Resources: top
The American Diabetes Association
Content last updated June 18, 2008
