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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 health care provider figure out whether you have a high risk of developing diabetes and whether lifestyle changes and medications such as Metformin might be helpful in treating your PCOS.
What is Glucose?
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 exactly is an Oral Glucose Tolerance Test (OGTT)?
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 fasting overnight and then having your blood checked early in the morning. Then you will drink a special sugar beverage and after 2 hours you will have your blood tested again. Sometimes blood sugar levels are also drawn at other times such as 1 hour, 3 hours, or 4 hours after the
glucose drink.
What if my blood glucose level is high?
If the OGTT shows that your blood glucose levels are higher than normal, your health care provider 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 an illness that can develop if your body does not make enough insulin, or when your body has difficulty using the insulin that it does make.
Your health care provider may suggest a fasting glucose level or an oral glucose test (especially if you are overweight). Depending on the results, these tests are often repeated every few years. |
What do I need to do before my OGTT?
Your health care provider 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 health care provider’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 you call your pharmacy ahead of time to check to see if they have the glucose drink in stock, because some pharmacies may not carry this item.
Do I need to eat anything special before the test?
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:
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 first thing in the morning, ie: at 8 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?
When you are ready to leave your home to have your test done, be sure to remember to bring:
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
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 for your next blood test (about 2 hours later). You may read, listen to music, talk, or do another quiet activity while you are 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?
The lab will usually send your results to your health care provider within a few days. You may already have a follow–up appointment scheduled or your health care provider may call you to review your results and let you know if there are any concerns.
What do the results mean?
The first test or "baseline" glucose test is your blood glucose level before you drank the glucose beverage. Normal fasting blood glucose levels are less than 100 mg/dl. Your health care provider may also check your insulin level. A high level of insulin means that your body does not use insulin well (even if your glucose levels are normal).
The second result of your 2–hour blood glucose test measures your glucose two hours after you drank the glucose beverage. This level should be less than 140mg/dl.
Normal levels of glucose mean that your body is able to use glucose the way it is supposed to.
High levels of glucose mean that you have impaired glucose tolerance (IGT). This means that your body has a hard time breaking down glucose, and puts you at risk for developing diabetes. If your glucose levels continue to be very high, it could mean that you have diabetes.
What is the connection between impaired glucose tolerance (IGT) and PCOS?
Health care providers 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 health care provider 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 health care provider is the best way to keep your body healthy. |
Resources:
The American Diabetes Association
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Updated: 8/25/2009
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