The oral glucose tolerance test (OGTT) is also known as the glucose tolerance test. It’s a 2-hour test to assess your body’s reaction to sugar (glucose).
Type 2 diabetes can be detected using the glucose tolerance test. A modified version of the glucose tolerance test is more commonly used to diagnose gestational diabetes, which is a type of diabetes that develops during pregnancy.
The test is made available to:
- Selected expectant mothers at 26 weeks;
- All expectant mothers with a history of diabetes at 16 weeks. At 26 weeks, the test will be repeated if the results at 16 weeks are normal.
- Any pregnant woman who exhibits diabetic symptoms, such as extra fluid surrounding the fetus or a large baby.
Why it’s done and the risks involved
The 2-hour glucose tolerance test finds issues with how your body processes glucose after a meal, frequently before your fasting blood glucose level does.
Getting a blood sample carries just a little amount of danger. You can have bleeding or bruising after having your blood drawn.
Additionally, you can experience fainting or a dizzy feeling. After your procedure, infection is a possibility in specific circumstances.
Getting ready for the GTT
- Maintain your regular diet for the week leading up to the test.
- The night before the exam, you are only permitted to consume water after 9.30 p.m. No other food or beverage is permitted.
- Only clear, flavorless water may be consumed before the test, you must refrain from eating or chewing gum.
Procedure to Conduct a 2-hour Oral Glucose Tolerance Test
- The glucose tolerance test takes about 2.5 hours.
- Here’s what to expect:
- When you arrive, a fasting blood sample will be taken from your arm.
- You’ll then drink a glucose solution with a specific amount of sugar.
- Two hours later, another blood sample will be taken from your arm.
- During the test:
- You can only drink plain water—no food or other drinks are allowed.
- Avoid smoking, as it can affect the test results.
- Stay at the hospital until the test is done. Try to stay still and avoid any physical activity.
- If permitted, you can wait in your parked car outside.
- After the test, you’re free to eat and drink as you normally would.
- The test is safe and carries no risks.
Results of 2-hour Glucose Tolerance Test:
Regarding the three-hour exam:
- A fasting blood glucose level of less than 95 mg/dL (5.3 mmol/L) is considered normal.
- A normal blood glucose level is less than 180 mg/dL (10 mmol/L) an hour after consuming the glucose solution.
- A normal blood glucose level is less than 155 mg/dL (8.6 mmol/L) two hours after consuming the glucose solution.
- A normal blood glucose level is less than 140 mg/dL (7.8 mmol/L) three hours after consuming the glucose solution [Ref].
If one of the results is higher than expected, you will most likely need to retest in four weeks. You will be diagnosed with gestational diabetes if two or more of the results are higher than normal.
One-hour Glucose Tolerance Test
The one-hour glucose tolerance test, often known as the glucose challenge test, gauges how your body reacts to sweets (glucose).
If you’re at average risk of gestational diabetes, you’ll likely be screened during your second trimester between 24 and 28 weeks of pregnancy. You can take the glucose challenge test without fasting beforehand.
Procedure to Conduct a 1-hour GTT
- The glucose challenge test is carried out in two stages.
- When you arrive at your doctor’s office or the lab, you’ll be given a syrupy glucose solution containing 1.8 ounces (50 grams) of sugar.
- You must wait for your blood sugar level to be measured in the lab or at the office of your healthcare practitioner. Other than water, you are not allowed to eat or drink anything during this time.
- A blood sample will be drawn an hour later from a vein in your arm. You’ll have your blood sugar level checked using this sample of blood.
Results of 1-hour GTT:
The glucose challenge test results are reported in millimoles per liter (mmol/L) or milligrams per deciliter (mg/dL).
- A normal blood sugar level is less than 140 mg/dL (7.8 mmol/L).
- When the blood sugar level ranges from 140 mg/dL (7.8 mmol/L) to less than 190 mg/dL (10.6 mmol/L), a three-hour glucose tolerance test is required to determine whether gestational diabetes is present.
- Gestational diabetes is identified by a blood sugar level of 190 (10.6 mmol/L) or above. Perhaps no additional testing is required.
- When screening for gestational diabetes, some clinics or labs utilize a lower threshold of 130 mg/dL (7.2 mmol/L).
If gestational diabetes is identified in you, you can avoid difficulties by closely monitoring your blood glucose level for the remainder of your pregnancy.
A two-hour glucose tolerance test should be administered to women with gestational diabetes 4 to 12 weeks after delivery, according to the American College of Obstetricians and Gynecologists [Ref].
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