What is the Gestational Glucose Tolerance Diagnostic Blood Test, and why do you need one?

A Gestational Glucose Tolerance Diagnostic Blood Test, 3-Hour is used to diagnose gestational diabetes. The science behind the test is to measure and determine the glucose concentration over three hours. The test is often recommended for pregnant women who might have symptoms or characteristics that might put them ask risk. The test is performed after orally ingesting 100 grams of a sweet drink called glucose. 

How Does the Test Work?

You can have the 3-hour blood glucose test in a local lab. The test person will last for an average of 13 hours, a maximum of 16 hours before the test.

A sample of the blood sugar will be collected, after which they give the candidate a bottle of glucose with high sugar content. (This contains 100 grams of sugar for women pregnant and 75 gram for others). The person will also be tested again after ½ hour, an hour, second (2) hours, and the third (3) hours after consuming the drink.

You need to be generally healthy to receive an accurate test for it to be reliable. If you have an underlining health condition, it could make the test results inaccurate. Also, to receive the most accurate readings being generally active and not sedentary days leading up to the test is recommended. Also, any medication that could alter the body’s glucose level could result in inaccurate results. 

What does the 3-hour blood glucose test tell you?

The three-hour blood glucose test involves measuring and determining blood glucose level 5 times within 3 hours. 

For someone free from diabetes, the blood glucose level will rise after the drink and go back to ideal levels quickly and tracks insulin production in response to the glucose. 

For a diabetic patient, the glucose level will rise way more than expected after taking the glucose. It will also proceed down to lower levels but much slower. This can be traced to two reasons: there is no insulin production, or the body cells can’t respond to the insulin. 

There are, however, possibilities that blood glucose tests during the three-hour test could vary. As a result, the doctor might order a repeat test provided the test reveals a slightly higher blood glucose level. 

How to Prepare for the test

Here are some preparations and precautions to take before the day of testing:

  • Fasting overnight is required, which will span between 8 to 14 hours, and the test is conducted in the morning after the fast
  • You should have at least three days of physical activity and a diet that contains more than 150 grams of carbs. 
  • Consume your normal meals before the testing day
  • You need to stay away from food, coffee, alcohol, or exercise 12 hours before your test. Water, however, is allowed.
  • Having someone drive you to the lab is optimal because sometimes the fasting could cause impairment.  
  • You might need up to four hours for the test. One needs to remain in the lab for the test as various activities can interfere with its accuracy.

What does the Result of the test Indicate?

There are many things a 3-hour glucose test might indicate. Expect any of the following:

Normal response: for normal response, the 2-hour glucose level will be equal to or lower than 110 mg/dL

Impaired Fasting Glucose: for someone with fasting glucose greater or equal to 100 and lower than 126 mg/dL, the person’s fasting glucose is impaired. Such a person has a risk of developing diabetes in the future, which will warrant a future test. The test, however, does not signify the presence of the ailment. 

Impaired Glucose Tolerance: for this, the person has their test equal to or more than 140 but not up to 200 mg/dL. Also, the person has a risk of future diabetes.

Diabetes: when the oral glucose test reveals that the level of blood glucose is higher than or the same as 200 mg/dL. It is, however, essential to have another test to confirm this.


James, Norman (2016) Diagnosing Diabetes. Retrieved from https://www.endocrineweb.com/conditions/diabetes/diagnosing-diabetes

Michael D ()2020. Do I Need an Oral Glucose Tolerance Test? Retrieved from https://www.webmd.com/diabetes/guide/oral-glucose-tolerance-test#1-4

More Land Obgyn (n/d). Instructions for 3 hours Glucose Tolerance Test. Retrieved from https://www.morelandobgyn.com/instructions-for-3-hour-glucose-tolerance-test#:~:text=Instructions%20for%203%2Dhour%20Glucose,total%20of%20four%20blood%20draws

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