Have you ever heard of a glucose tolerance test, or GTT for short? Your doctor may have told you about it, or you may have even asked to have it done. This is a very important test that checks whether your body is actually using or storing sugar, or glucose. Doctors often use this test to diagnose conditions like diabetes. But there are other ways to diagnose diabetes, such as the A1C test and the fasting blood sugar test.
So, what is this glucose tolerance test (`GTT`)?
Simply put, our bodies get their energy from the food we eat, especially foods high in carbohydrates. This is what gives our cells the energy to function. Our bodies also store this glucose for later use, mainly in our muscles and liver. This stored glucose is called glycogen.
So, to keep the glucose level in our blood at a certain level, various processes take place inside our body. Among them , the hormone called insulin plays the main role . This insulin is produced in our pancreas. If there is any problem in the way our body uses glucose, the blood sugar level can often increase. That is what we call hyperglycemia. Also, sometimes the blood sugar level can decrease, and that condition is called hypoglycemia.
There are different types of GTT. The most commonly used is the Oral Glucose Tolerance Test (OGTT), which involves giving a glucose solution by mouth.
It's normal to feel a little nervous before any medical test. But remember, the most important thing is to be informed. Whatever the results, you'll learn more about your body than you ever knew before. With that information, you and your doctor can make the best plan for your health going forward.
In what situations would you need to do this `(GTT)`?
Your doctor may suggest a GTT to check for or confirm the presence of any of the following conditions:
- Diabetes – often prediabetes, type 2 diabetes, or gestational diabetes.
- A condition called insulin resistance.
- Reactive hypoglycemia – This is a decrease in blood sugar levels after eating.
- Acromegaly is a hormonal condition.
- Rare carbohydrate metabolism disorders.
But keep in mind that there are other tests that can be used to diagnose these conditions. Your doctor may order more than one test.
Especially during pregnancy, a one-hour glucose challenge test is usually done to check for gestational diabetes . If the results are abnormal, your doctor may order a three-hour oral glucose tolerance test (OGTT) to confirm the diagnosis or rule out the condition.
How exactly should one prepare for a `(GTT)`?
Since there are several types of GTT, there may be slight variations in how you need to prepare depending on the test you are taking. But in general, here are the things you need to do:
- You should tell your doctor about all the medications and supplements you are taking, as some medications can affect the test results. Your doctor may ask you to stop taking certain medications a few days before the test.
- You should eat normally for at least three days before the test. It is important to eat foods that provide at least 150 grams of carbohydrates per day.
- Do not change your normal daily activities or exercise routine for at least three days . Do not suddenly engage in strenuous exercise before the test.
- You will need to fast before the test – this means you cannot eat or drink anything other than water for at least 8 hours (maybe more).
- You cannot eat or smoke during the entire test.
Your doctor will give you a clear set of instructions on exactly what to do based on your condition and the type of GTT you are having. It is very important to follow them exactly. If you have any questions or don't understand something, don't hesitate to ask your doctor, okay?
What happens on the day of the `(GTT)`?
We've already discussed how the ``GTT'' can vary depending on the type of test. Let's take an example of how the most commonly performed two-hour ``Oral Glucose Tolerance Test - OGTT'' is performed.
Most of the time, this test starts in the morning, usually between 7:00 and 9:00 a.m. Since you will be at the hospital or medical center until the test is over, it is wise to bring something to keep you occupied, such as a book or notebook.
These are the steps that usually happen:
1. First, a doctor or a phlebotomist will take a blood sample from your vein. This is used to measure your fasting blood glucose level.
2. Then, you will be given a special glucose solution to drink. This usually contains about 75 grams of glucose dissolved in 250-300 milliliters of water. You will be instructed to drink all of this solution within five minutes. However, the amount of glucose given to young children and pregnant women may vary. This glucose solution is very sweet, like a sweetened Gatorade. Some people may find the taste a little unpleasant.
3. Exactly two hours after drinking the glucose solution, another blood sample will be taken from your vein to check your blood glucose level. Depending on the reason for the test, blood may be taken every 30 minutes, once an hour, or several times after drinking the glucose solution.
Are there other variants of `(GTT)`?
Yes, there are several variants of `(GTT)` tailored to different needs. Let's look at a few examples:
- One-hour glucose tolerance test: This is often done to screen for gestational diabetes. You drink a liquid containing 50 grams of glucose, and then your blood sugar level is measured one hour later. This test usually does not require fasting.
- Three-hour glucose tolerance test: In this test, blood is taken before drinking a glucose solution (after fasting). Then, blood samples are taken again one hour, two hours, and three hours after drinking the glucose solution.
- Glucose tolerance test for acromegaly: In this test, your doctor takes a blood sample not to check your blood sugar level, but to check your levels of human growth hormone (HGH). After you drink the glucose solution, your blood may be drawn every 30 minutes for two hours (that is, at 30, 60, 90, and 120 minutes).
What to expect after the test is over?
After the GTT, you can go about your daily activities as usual. You can also start eating again. It may be a good idea to bring a snack to eat after the test. Your doctor will tell you if there are any special instructions, and will also let you know when the results will be available.
How long does it take to know the test results?
In most cases, you will be able to get the results of the ``GTT'' within a few working days. However, this time can vary slightly from lab to lab. So don't worry.
Are there any side effects from this `(GTT)`?
A glucose tolerance test is generally a very safe test . Most people do not feel any discomfort after drinking the glucose solution. However, some people may feel a little nauseous or dizzy. However, serious side effects are rare.
Blood draws are a very common and necessary part of medical testing. They don't pose any major risks. You may feel a little sore or a little bruised, but they will heal quickly.
What do the `(GTT)` results really say?
Your GTT results report will show the blood glucose level at each time your blood was drawn. In Sri Lanka, blood glucose is usually measured in milligrams per deciliter (mg/dL).
The ranges used by different labs and doctors to diagnose blood sugar problems like diabetes can vary slightly, so always refer to the reference range provided on your results report.
In general, doctors use these ranges of values for a two-hour OGTT:
- Normal: Less than 140 mg/dL.
- Prediabetes: Between 140 mg/dL and 199 mg/dL.
- Diabetes: 200 mg/dL or higher.
These values and blood sampling intervals may vary for other conditions, such as gestational diabetes and acromegaly. For example, the growth hormone test (GTT) to check for acromegaly assesses changes in growth hormone levels. Your doctor will discuss these results with you in detail.
If the results are abnormal, what happens next?
Imagine, what happens next if your `(GTT)` results are not normal, that is, `abnormal`. Don't worry, your doctor will clearly tell you what steps to take next. True, it is normal to feel a little worried and scared when a result is abnormal. But know this, doctors do not immediately decide that you have `prediabetes` or `diabetes` just because one `(OGTT)` result is abnormal.
You will likely need to have the same test again in a few days, or your doctor may also order another diagnostic test, such as an A1C test. However, your doctor will be with you throughout the entire diagnostic process. Don't hesitate to ask any questions you have and talk about your concerns.
It's normal to feel scared when you see an abnormal test result. But remember, an abnormal GTT result doesn't necessarily mean you have diabetes. If the results show that your blood sugar is high, your doctor will likely do further tests to make a definitive diagnosis. Don't be afraid to ask your doctor questions. They are there to help you.
The most important things we should take home from this story
So, the Glucose Tolerance Test (GTT) that we talked about today is a very important medical test that helps us know exactly how our body uses and stores sugar, that is, glucose. This is especially helpful in early detection of diseases like diabetes.
There is a little preparation before the test, and following it exactly is very important for accurate results. During the test, you will drink a sweet glucose liquid, and then blood samples will be taken several times over a few hours.
The most important thing is not to panic, no matter what the results are . Even if the results are abnormal, it is not the end of the world. Talk to your doctor carefully and find out exactly what to do next. Remember, early detection and treatment of medical conditions is the best way to live a healthy, happy life! If you have any questions, don't hesitate to talk to a doctor.
` Glucose Tolerance Test, GTT, OGTT, Diabetes, Sugar Test, Gestational Diabetes, Blood Glucose
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