A Glucose Tolerance Test: What Is It?
An oral glucose tolerance test evaluates your body’s ability to metabolize sugar. If the test indicates that your level is excessively high, it indicates that your cells are not properly absorbing sugar.
Your doctor can use the test to determine whether you already have diabetes or whether you are at risk for developing it. An abbreviated OGTT is used to screen for gestational diabetes, a type of diabetes that develops during pregnancy.
Typically, eating causes your blood sugar to rise. Insulin is a hormone released by the pancreas, a lengthy gland located deep within your abdomen. It facilitates the transfer of blood sugar into cells for storage and energy. After then, your blood sugar returns to normal.
Your body does not use insulin well if you have type 2 diabetes. Blood glucose levels rise. Your body’s blood vessels may sustain harm from this much sugar. Diabetes can cause kidney damage, eye problems, nerve damage, and heart disease.
Why Perform a Glucose Tolerance Test?
An oral glucose tolerance test may be necessary if you:
- Are you obese or overweight?
- Have a close relative who has diabetes?
- Possess elevated blood pressure
- Possess elevated triglycerides, a form of blood fat.
- Possess PCOS, or polycystic ovarian syndrome, which results in irregular periods.
- Gave birth to a child weighing over nine pounds.
- Suffered from gestational diabetes while pregnant
Glucose Tolerance Test during Pregnancy
A shortened version of the oral glucose tolerance test will likely be administered to expectant mothers between weeks 24 and 28 of their pregnancy. The glucose challenge test is the abbreviated kind that just takes an hour to complete.
Risk factors consist of:
- Previously experiencing gestational diabetes during pregnancy
- A history of diabetes in the family
- Being overweight
- Another illness, such metabolic syndrome or PCOS, that increases your risk of developing diabetes
Your doctor will likely ask you to do a different version of the glucose challenge test if they are worried about your risk or if you have an abnormal level on the test.
Preparation for a Glucose Tolerance Test
Maintain your usual dietary habits in the days preceding the test.
Refrain from consuming any food for 8 hours prior to the test. It is advisable to schedule it first thing in the morning to facilitate overnight fasting. During the eight-hour period, you should consume only water. Discuss any drugs you are taking with your doctor when scheduling the test.
Procedure for Glucose Tolerance Test
The OGTT will be administered at your physician’s office, a clinic, hospital, or laboratory. The initial step is obtaining a blood sample. This will determine your fasting blood glucose level.
You will have a substantial glass of a sweetened mixture. When conducting the test on a child, the volume of liquid consumed is modified to correspond with their body weight.
If the examination is assessing for type 2 diabetes, a blood sample will be collected again two hours following the ingestion of the liquid.
Pregnant individuals may be required to undergo an extended oral glucose tolerance test. Your physician may request this due to your elevated risk of developing gestational diabetes or because your results from the 1-hour glucose challenge test raised concerns.
You will fast for 8 hours and undergo a blood sample collection to determine your fasting blood glucose level. Subsequently, blood samples will be collected at 1, 2, and 3 hours following the consumption of the sugary solution.
You will likely need to wait at the physician’s office or laboratory for the duration of the test. Upon completion of the test, you may immediately resume your regular activities.
Risks Associated with the Glucose Tolerance Test
The OGTT presents little complications. Certain individuals experience mild adverse effects from the sugary beverage or the injection.
Side effects of the drink include:
- Nausea, vomiting, bloating
- Headache.
- Hypoglycemia (infrequent)
Potential issues arising from the blood test encompass:
- Profuse hemorrhaging
- Syncope Infection
- Multiple attempts to locate a vein may cause minor discomfort
- Bruising or tenderness at the injection site.
Results of the Glucose Tolerance Test
Your blood glucose level is expected to increase following the consumption of the sugary beverage. Subsequently, it should return to baseline, as insulin facilitates the transport of glucose into your cells. If your blood glucose levels require an extended period to normalize, you may have diabetes.
Normal range for glucose tolerance test
The standard range for blood glucose is 139 mg/dL or less.
A glucose level between 140 mg/dL and 199 mg/dL indicates poor glucose tolerance. This condition is also referred to as prediabetes. You are at risk of developing type 2 diabetes. Your risk of cardiovascular disease is heightened, even in the absence of diabetes.
A blood glucose level of 200 mg/dL or above may indicate diabetes.
The standard range for non-pregnant individuals can be further delineated:
- The standard fasting glucose level ranges from 60 to 99 mg/dL.
- At the one-hour interval, a normal level is below 200 mg/dL.
Normal range for glucose challenge test
For pregnant individuals undergoing the 1-hour glucose challenge test to assess for gestational diabetes, a normal result is below 140 mg/dL.
A blood glucose level exceeding 199 mg/dL after the 1-hour test indicates gestational diabetes.
For the three-hour test to assess gestational diabetes, the following ranges apply:
- A standard fasting blood glucose level is below 95 mg/dL.
- At the one-hour interval, a normal level is below 180 mg/dL.
- At the two-hour interval, a normal level is below 155 mg/dL.
- At the three-hour interval, a normal level is below 140 mg/dL.
If any of your results are elevated, your physician will request a retest in a few weeks. Two or more elevated values indicate gestational diabetes.
What’s Going to Happen?
If you have prediabetes, your physician will discuss strategies to prevent its progression to diabetes. Engaging in physical activity and reducing body weight are two methods to diminish the risk of developing type 2 diabetes.
If the test indicates diabetes, you may undergo an A1c test or further assessments to verify the diagnosis. Nutrition, physical activity, and pharmacotherapy can assist in regulating your blood glucose levels.
Nutrient-rich diets and regular physical activity can assist in managing diabetes during pregnancy. Your blood glucose levels should return to normal following the birth of your child.
Gestational diabetes elevates the chance of developing type 2 diabetes post-pregnancy. Adhering to a nutritious diet and a consistent exercise regimen is essential to prevent a future diabetes diagnosis.
Key Insights
An oral glucose tolerance test, or OGTT, evaluates the body’s ability to metabolize sugar. Your results may indicate that you are at risk for type 2 diabetes or that you are already diagnosed with it. Pregnant individuals will undergo glucose tolerance testing to ascertain the absence of gestational diabetes. For the test, you undergo an 8-hour fast followed by a blood draw to determine your fasting glucose level. Depending on the specific test administered, blood will be collected again after 1, 2, or 3 hours. The dangers associated with the tests are negligible, and you may resume your regular activities immediately thereafter.
Frequently Asked Questions about the Glucose Tolerance Test
What is the duration of fasting for an OGTT?
Your final meal must occur no less than 8 hours prior to your examination. It is advisable to schedule it first thing in the morning to ensure an overnight fast. Water is permitted, but no other liquids are allowed.
What is the method to successfully complete the OGTT?
A normal blood glucose level in this test is 139 mg/dL or below.
What distinguishes OGTT from GTT?
The oral glucose tolerance test (OGTT) is occasionally referred to as a glucose tolerance test (GTT). The abbreviated, 1-hour variant of the examination is referred to as the glucose challenge test.