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Glucose Tolerance Test (GTT)

The term GTT stands for Glucose Tolerance Test. This test is performed to determine how well and properly

The term GTT stands for Glucose Tolerance Test. This test is performed to determine how well and properly the body cells of a patient are able to absorb sugar/glucose after ingesting a certain amount of sugar.

How the test works

This test works by comparing the sugar levels of glucose before and after the ingestion of sugar/sugary substance or solution. Before performing the test, the doctor/ health provider will ask the patient not to eat for a certain amount of time prior to the test. It is worth mentioning that the patient should eat according to his/her regular habit before the fasting period.

At the time of collecting the blood sample, the patient has to go to the doctor’s office or a local lab where a technician will collect the blood sample. The sample will be used to determine the baseline glucose level. Then, the patient will be given a sugary drink to ingest and wait for a couple of hours. The patient will be advised to remain sitting or lying down and keep themselves busy with reading a book, magazine or newspaper so as to avoid too much walking around as this might result in false results as the body will breakdown/utilize the sugar at a faster rate than it would normally.

After the set period, another sample of blood with be collected. Generally, the body quickly moves glucose into the cells. This reduces the glucose level to normal. If there’s any problem doing so, glucose will remain in the bloodstream and the second blood sample will have its signature.

From the second blood sample, the amount of blood sugar determines the result.

 

 

Type 2 diabetes

If you’re being tested for type 2 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 between 140 and 199 mg/dL (7.8 and 11 mmol/L) is considered impaired glucose tolerance, or prediabetes. If you have prediabetes, you’re at risk of eventually developing type 2 diabetes. You’re also at risk of developing heart disease, even if you don’t develop diabetes.
  • A blood glucose level of 200 mg/dL (11.1 mmol/L) or higher may indicate diabetes.

If the results of your glucose tolerance test indicate type 2 diabetes, your doctor may repeat the test on another day or use another blood test to confirm the diagnosis. Various factors can affect the accuracy of the glucose tolerance test, including illness, activity level and certain medications.

Gestational diabetes

If you’re being tested for gestational diabetes, your doctor will consider the results of each blood glucose test.

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.

For the three-hour test:

  • A normal fasting blood glucose level is lower than 95 mg/dL (5.3 mmol/L).
  • One hour after drinking the glucose solution, a normal blood glucose level is lower than 180 mg/dL (10 mmol/L).
  • Two hours after drinking the glucose solution, a normal blood glucose level is lower than 155 mg/dL (8.6 mmol/L).
  • Three hours after drinking the glucose solution, a normal blood glucose level is lower than 140 mg/dL (7.8 mmol/L).

If one of the results is higher than normal, you’ll likely need to test again in four weeks. If two or more of the results are higher than normal, you’ll be diagnosed with gestational diabetes.

If you’re diagnosed with gestational diabetes, you can prevent complications by carefully managing your blood glucose level throughout the rest of your pregnancy.

Why it is needed?

The purpose of this test is to detect diabetes. Generally, normal blood tests can identify whether a person has diabetes or not.

However, some people show borderline results. The borderline is the border between diabetes and non-diabetes condition. Moreover, if the doctor suspects type-2 diabetes, GTT is very effective. This test is also performed for diagnosing diabetes during pregnancy or identify pre-diabetes (impaired glucose tolerance).

A healthy person will have a controlled level of sugar in the blood. Normally, after taking a meal, the sugar level rises but soon, it goes down to the normal level as the additional glucose is used or stored in the body. In the case of pre-diabetes, the body can’t handle blood sugar level well after a certain limit. However, pre-diabetes isn’t diabetes, but on the brink of it. This test helps determine the proper pattern of diabetes/pre-diabetes.

In the case of pregnant women, diabetes can cause complications. That’s why determining diabetes early is important. The doctor may suggest the test between the 24th & 28th week. If the symptoms of diabetes/pre-diabetes are seen, the doctor may suggest the test earlier.

Are there any side-effects?

As the test is performed by collecting a blood sample, there is hardly any chance for any occurrence. However, a small bruise will remain at the point of needle’s insertion. A rare case is a swollen vein. Within a few days, these symptoms are expected to go away.

The sugary drink may cause some problems to the patient including –

  • Vomiting
  • Bloating
  • Nausea
  • Headache
  • Low blood sugar (rare scenario)

For more interesting information on GTT:

https://www.mayoclinic.org/tests-procedures/glucose-tolerance-test/about/pac-20394296

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