The Glucose Tolerance Test (GTT) is a diagnostic test that is used to measure how well your body processes sugar. The test is commonly used to diagnose gestational diabetes, which is a type of diabetes that develops during pregnancy. The GTT can also be used to diagnose diabetes and other conditions related to how your body processes sugar. In this article, we will discuss how to prepare for the GTT.
What is the Glucose Tolerance Test (GTT)?
The GTT is a diagnostic test that measures how well your body processes sugar. The test involves drinking a sugary drink and having your blood sugar levels checked at regular intervals. The test is commonly used to diagnose gestational diabetes, but it can also be used to diagnose other conditions related to how your body processes sugar.
The test is usually performed in the morning, after an overnight fast. You will be asked not to eat or drink anything except water for at least 8 hours before the test. This is because eating or drinking anything other than water can affect your blood sugar levels and the accuracy of the test.
What are the Significance of Glucose Tolerance Test (GTT)?
Here are some possible significance of the glucose tolerance test:
- Diagnosis of diabetes: The glucose tolerance test is used to diagnose diabetes and impaired glucose tolerance (IGT), which is a pre-diabetic condition.
- Evaluation of insulin resistance: The glucose tolerance test can help evaluate insulin resistance, which is a condition in which the body's cells become resistant to insulin and unable to use glucose effectively.
- Monitoring gestational diabetes: The glucose tolerance test is used to monitor gestational diabetes, a type of diabetes that occurs during pregnancy.
- Assessment of hypoglycemia: The glucose tolerance test can help assess hypoglycemia, which is a condition characterized by low blood sugar levels.
- Identification of reactive hypoglycemia: The glucose tolerance test can help identify reactive hypoglycemia, a condition in which the body overreacts to high blood sugar levels by producing too much insulin, resulting in low blood sugar levels.
- Evaluation of metabolic syndrome: The glucose tolerance test can help evaluate metabolic syndrome, a cluster of conditions that increase the risk of heart disease, stroke, and diabetes.
- Assessment of cardiovascular risk: The glucose tolerance test can help assess cardiovascular risk by evaluating the body's response to glucose and insulin.
How to Test for GTT?
The glucose tolerance test (GTT) is used to assess how your body processes glucose. It can help diagnose type 2 diabetes and prediabetes. Here's how to prepare for and undergo the GTT test:
Preparation
- Fast overnight and schedule the test for early the following morning.
- Do not eat or drink anything for at least 8 hours before the test.
- Inform your healthcare provider about any medications you are taking, as some may need to be stopped before the test.
Procedure
- A blood sample will be taken to measure your fasting blood glucose level.
- You will drink a syrupy glucose solution containing 2.6 ounces (75 grams) of sugar.
- Your blood glucose level will be measured again after 2 hours.
Results
- A normal blood glucose level is lower than 140 mg/dL (7.8 mmol/L) after 2 hours.
- A blood glucose level between 140 and 199 mg/dL (7.8 and 11 mmol/L) is considered impaired glucose tolerance, or prediabetes.
- A blood glucose level of 200 mg/dL (11.1 mmol/L) or higher may indicate diabetes.
Gestational Diabetes
- If you're being tested for gestational diabetes, your doctor will consider the results of each blood glucose test.
- At Mayo Clinic, if your blood glucose level is higher than 140 mg/dL (7.8 mmol/L) after the one-hour test, your doctor will recommend the three-hour test.
- If your blood glucose level is higher than 190 mg/dL (10.6 mmol/L) after the one-hour test, you'll be diagnosed with gestational diabetes.
Three-Hour Test
- For the three-hour test, you will be asked to come to the test fasting (not having had anything to eat or drink for the previous eight hours).
- A fasting blood sugar will be obtained.
- You'll drink about 8 ounces (237 milliliters) of a glucose solution containing 3.5 ounces (100 grams) of sugar.
- Your blood glucose level will be tested again one, two, and three hours after you drink the solution.
After the Procedure
- You can return to your usual activities immediately after the test.
- Results are given in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).
Risks and Considerations
- The test may cause bruising or bleeding at the injection site.
- In some cases, infection after the procedure is possible.
- Factors like illness, activity level, and certain medications can affect the accuracy of the test.
Gestational Diabetes
- If you're being tested for gestational diabetes, your doctor will consider the results of each blood glucose test.
- At Mayo Clinic, if your blood glucose level is higher than 140 mg/dL (7.8 mmol/L) after the one-hour test, your doctor will recommend the three-hour test.
- If your blood glucose level is higher than 190 mg/dL (10.6 mmol/L) after the one-hour test, you'll be diagnosed with gestational diabetes.
Three-Hour Test
- For the three-hour test, you will be asked to come to the test fasting (not having had anything to eat or drink for the previous eight hours).
- A fasting blood sugar will be obtained.
- You'll drink about 8 ounces (237 milliliters) of a glucose solution containing 3.5 ounces (100 grams) of sugar.
- Your blood glucose level will be tested again one, two, and three hours after you drink the solution.
After the Procedure
- You can return to your usual activities immediately after the test.
- Results are given in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).
Risks and Considerations
- The test may cause bruising or bleeding at the injection site.
- In some cases, infection after the procedure is possible.
- Factors like illness, activity level, and certain medications can affect the accuracy of the test.
How to Prepare for the Glucose Tolerance Test (GTT)?
If you have been scheduled for a GTT, it is important to prepare for the test properly to ensure accurate results. Here are some steps you can take to prepare for the GTT:
- Talk to your doctor: Before you have the GTT, it is important to talk to your doctor about any medications you are taking. Some medications can affect your blood sugar levels and the accuracy of the test. Your doctor may advise you to stop taking certain medications before the test. It is also important to tell your doctor about any medical conditions you have, such as liver disease or kidney disease, as these can affect the results of the test.
- Follow your doctor’s instructions: Your doctor will give you specific instructions on how to prepare for the GTT. It is important to follow these instructions carefully to ensure accurate results. Your doctor may advise you to:
- Fast for at least 8 hours before the test: Avoid any foods or drinks that contain sugar for at least 24 hours before the test
- Avoid strenuous exercise for at least 24 hours before the test
- Avoid smoking or drinking alcohol for at least 24 hours before the test
- Plan: The GTT can take several hours, so it is important to plan. Make sure you have enough time in your schedule to complete the test. You may also want to bring a book or something to occupy your time while you are waiting.
- Keep light food: It is also a good idea to bring a snack with you, in case you need to eat something after the test. Your blood sugar levels may be low after the test, and eating a snack can help prevent low blood sugar.
- Dress comfortably: You will be sitting for many hours during the GTT, so it is important to dress comfortably. Wear loose-fitting clothing that will not constrict your blood flow.
During the GTT
During the GTT, you will be asked to drink a sugary drink. This drink contains a measured amount of glucose, which is a type of sugar. After you drink the sugary drink, your blood sugar levels will be checked at regular intervals.
The test usually involves having your blood drawn many times over many hours. The exact number of blood draws and the intervals between them will depend on your doctor’s instructions.
The GTT can be uncomfortable for some people, as sitting for many hours and having blood drawn multiple times can be unpleasant. However, it is important to follow through with the test to ensure accurate results.
After the GTT
After the GTT, you may feel tired or light-headed. This is normal and should go away after you eat something.
It is important to eat something after the test to prevent low blood sugar. Your doctor may recommend a specific type of food to eat, such as a carbohydrate-rich snack or meal.
You should also drink plenty of water after the test to help flush out the excess glucose from your body. It is important to follow any instructions given to you by your doctor after the test.
Interpreting the Results
After the GTT, your doctor will interpret the results to determine if you have any conditions related to how your body processes sugar. The results of the GTT will show how your body responds to the sugary drink.
If your blood sugar levels remain within normal range throughout the test, it is unlikely that you have any conditions related to how your body processes sugar. However, if your blood sugar levels are elevated at any point during the test, it may indicate that you have a condition such as gestational diabetes or diabetes.
If you are diagnosed with a condition related to how your body processes sugar, your doctor will work with you to develop a treatment plan. This may involve changes to your diet, exercise routine, or medication.
GTT Test Normal Range in Pregnancy
The normal range for the glucose tolerance test (GTT) during pregnancy is as follows:
- Fasting glucose: less than 92 mg/dL (5.1 mmol/L)
- 1-hour glucose: less than 180 mg/dL (10.0 mmol/L)
- 2-hour glucose: less than 153 mg/dL (8.5 mmol/L)
However, the normal range may vary slightly depending on the laboratory and the specific testing protocol used. It is important to consult with your healthcare provider for the interpretation of your specific test results.
Glucose Tolerance Test at Home
A glucose tolerance test typically requires specialized equipment and trained medical personnel to administer and monitor the test accurately. It is not recommended to perform a glucose tolerance test at home without medical supervision. In case of any concerns regarding blood sugar levels, it is important to consult a healthcare professional who can advise on the appropriate testing and monitoring methods.
Difference Between Oral Glucose Tolerance Test (OGTT) or Glucose Tolerance Test (GTT)
The terms Oral Glucose Tolerance Test (OGTT) and Glucose Tolerance Test (GTT) are often used interchangeably to refer to the same diagnostic test. However, there is a subtle difference between the two terms.
- The Glucose Tolerance Test (GTT) is a general term used to describe any test that measures how well your body processes sugar. This can include tests that use different types of sugar, such as glucose or fructose.
- The Oral Glucose Tolerance Test (OGTT) is a specific type of Glucose Tolerance Test that involves drinking a sugary drink containing a measured amount of glucose. The OGTT is used to diagnose diabetes and gestational diabetes, as well as other conditions related to how your body processes sugar.
- During the OGTT, you will be asked to fast for at least 8 hours before the test. Then, you will drink a sugary drink containing a measured amount of glucose. Your blood sugar levels will be checked at regular intervals for several hours to see how your body processes the sugar.
- The OGTT is commonly used to diagnose gestational diabetes, which is a type of diabetes that develops during pregnancy. It is also used to diagnose diabetes and other conditions related to how your body processes sugar.
In contrast, other types of GTT may involve different types of sugar, such as fructose. These tests may be used to diagnose conditions other than diabetes, such as hereditary fructose intolerance.
What can you eat before a GTT test?
You will need to be fasting for 8 to 12 hours before your GTT test with no food or drinks besides water. Follow your testing center's guidelines on the exact fasting period required beforehand, as it can vary. Avoid coffee, tea, gum and mints.
Can I drink water before a GTT test?
Yes, you are encouraged to drink regular water during the fasting period leading up to your GTT. Staying well-hydrated with water before the sugar solution drink and blood test is important. Avoid any other beverages besides plain water.
What is considered failing a GTT test?
The criteria for passing/failing a GTT test depends on the exact type done. For a standard test, blood sugar levels under 140 mg/DL at the 1 hour mark and below 200 mg/DL at the 2 hour mark is generally within normal limits to pass the test. Higher readings could indicate issues like diabetes or prediabetes.
How long does it take to get GTT test results?
Most laboratories process GTT test results within a few days of the lab receiving your blood samples. However, turnaround times can vary. Check with your healthcare provider’s office when your personal GTT results are expected to be available for discussion and next steps based on the outcome.
Conclusion
The OGTT is a specific type of Glucose Tolerance Test that involves drinking a sugary drink containing a measured amount of glucose. The OGTT is used to diagnose diabetes and gestational diabetes, as well as other conditions related to how your body processes sugar. Other types of GTT may involve different types of sugar and may be used to diagnose conditions other than diabetes.
Preparing for the GTT is important to ensure accurate results. Follow your doctor’s instructions carefully and plan to make the process as comfortable as possible. If you are diagnosed with a condition related to how your body processes sugar, work with your doctor to develop a treatment plan that is right for you.
Remember, the GTT is a diagnostic test that can help detect conditions early, which can lead to better outcomes. If you have any concerns about the GTT or your overall health, talk to your doctor. They can provide you with the information and guidance you need to stay healthy.
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