Glucose Tolerance Test

1 What is a Glucose Tolerance Test?

A test that measures your body’s response to glucose is called glucose tolerance test or oral glucose tolerance test.

This test can detect type 2 diabetes and a modified version of the glucose test can be used to diagnose gestational diabetes which is a type of diabetes that you can have during pregnancy.

2 Reasons for Procedure

The main reason for a glucose tolerance test is identifying abnormalities in how your body takes glucose after a meal and is often done before your fasting blood glucose level becomes abnormal.

3 Potential Risks

Glucose tolerance test is considered safe but there may be side effects or potential risks, though rare:

  • excess bleeding from the area was punctured
  • infection if the area is not properly sterilized before the sample is taken
  • feeling light-headed
  • bruising and swelling where the needle was inserted

4 Preparing for your Procedure

To prepare for your glucose tolerance test, you should eat and drink normally and you should tell your doctor if you are taking any medications or if you are sick because these factors may affect the results of your test.

Your doctor may ask you not to eat and drink anything for 8 hours before the test or he may even ask you to fast overnight.

5 What to Expect

Read on to learn more about what to expect from your glucose tolerance test.

This is done by several steps. Your doctor will take a sample of blood from a vein in your arm and this will be used to measure your fasting blood glucose level.

If your doctor is testing you for type 2 diabetes, he will ask you to drink about 8 ounces or 237 milliliters of a syrupy glucose solution that contains 2.6 ounces or 75 grams of sugar, and then 2 hours later he will measure your blood glucose level again.

The test for gestational diabetes in low-risk pregnant women between the 24th and 28th weeks of pregnancy is a 1-hour blood glucose challenge test according to the American Congress of Obstetricians and Gynecologists.

The risk factors for gestational diabetes include:

Your doctor may even recommend three-hour glucose tolerance test if you are at risk or you have a suspicious value one-hour test.

The three-hour test:

  • your doctor will ask you to fast or not eat or drink anything 8 hours before the test
  • during the test, he will ask you to drink about 8 ounces or 237 milliliters of a glucose solution containing 3.5 ounces or 100 grams of sugar
  • he will test your blood glucose level again two to three hours after you drink the solution

You can return to your normal activities after the test.

6 Procedure Results

The results of glucose tolerance test are given in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).

If you are tested for type two diabetes, two hours after drinking the glucose solution:

  • a normal blood glucose level is lower than 140 mg/dL (7.8 mmol/L)
  • a blood glucose level of 200 mg/dL (11.1 mmol/L) or higher may indicate diabetes
  • a blood glucose level between 140 mg/dL and 199 mg/dL (7.8 and 11 mmol/L) is considered prediabetes which can lead to type 2 diabetes or you may be at risk of developing heart disease

Your doctor may recommend repeating the test on another day or another blood test to confirm the diagnosis of you the results indicate that you have type 2 diabetes.

Your doctor will consider the results of each blood glucose test if you are being tested for gestational diabetes.

Your doctor will suggest the three-hour test if your blood glucose level is higher than 140 mg/dL (7.8 mmol/L) after the one-hour test.

Your doctor will diagnose you with gestational diabetes if your blood glucose level is higher than 190 mg/dL (10.6 mmol/L) after the one-hour test.

For the three hour test:

  • a normal fasting blood glucose level is lower than 95 mg/dL (5.3 mmol/L)
  • a normal blood glucose level is lower than 180 mg/dL (10 mmol/L) one hour after drinking the glucose solution
  • a normal blood glucose level is lower than 155 mg/dL (8.6 mmol/L) two hours after drinking the glucose solution
  • a normal blood glucose level is lower than 140 mg/dL (7.8 mmol/L) three hours after drinking the glucose solution

You will be tested again in four weeks if one of the tests is higher than normal or you will be diagnosed with gestational diabetes if two or more tests are higher than normal.

You can prevent complications by carefully managing your blood glucose level throughout the rest of your pregnancy if you are diagnosed with gestational diabetes.

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