How does GTT tolerance test work?

A glucose tolerance test evaluates how to manage the sugar situation after a meal. Glucose is a kind of sugar that results from the breakdown of carbohydrates in foods. Some of this sugar is used to produce energy, and the rest is saved for days and conditions. The amount of glucose is regulated by insulin and glucan hormones.

If the amount of sugar is high, the pancreas secretes more insulin to absorb the sugar and store it. And if the amount of blood sugar is low, the pancreas secretes the glucagon hormone to release stored sugary sugars and pours it into the bloodstream. The body performs all these actions to maintain balance. If part of the cycle is in trouble, blood glucose levels and diabetes will develop.

What is GTT testing done for?
Blood glucose testing is used to diagnose diabetes, gestational diabetes, or pre-diabetes. Of course, glucose tolerance testing can be perfectly safe for adults and children. Performing this test requires drinking a sweet solution after a fasting period. A blood sample will be taken from the bloodstream to evaluate the cleansing of sugar.

Blood glucose tolerance testing is more sensitive than other blood glucose tests to detect these inconsistencies and to imbalance in blood glucose. The blood glucose tolerance test is only applicable for screening and diagnosis and has no role in diabetes assessment or prediabetes. Among all the applications of blood glucose tolerance testing, this test can be used to diagnose:

Hypoglycaemia (a condition in which blood glucose falls immediately after eating)
Acromegaly (Pituitary gland filling)
Functional abnormalities of beta cells (conditions in which insulin is not well secreted)
And a very rare disorder called fetal intolerance, which affects glucose metabolism.
Types of oral glucose tolerance testing OGTT
This test can be based on the experimental objectives, which can be done in a variety of ways. The concentration of glucose solution, the time and number of blood samples will be different. Standard duality is used for screening and diagnostic purposes:

Two hours: This test is done with two blood transfusions to diagnose diabetes and pre-diabetes in non-pregnant, adult and pediatric patients.
Three hours: This test uses 4 blood samples to screen for gestational diabetes.
Pregnancy recommendations
This test is recommended as a routine screening test to diagnose gestational diabetes between weeks 24 and 28 of gestational age. Of course, some doctors often recommend a one-hour glucose tolerance test instead of a fasting method instead of a three-hour method. This one-hour test can be given before the 24th week in the presence of overweight, having a family history of diabetes, or in women with polycystic ovary syndrome, or in women with a history of gestational diabetes in the past.

If this test was conducted with unusual blood glucose results, such as equal or greater than 140 mg, a full three hour blood test would be required. Some physicians consider this amount to be 130 milligrams.

Advantages and disadvantages of GTT testing
Despite the sensitivity of this test to fasting blood glucose testing and the ability to diagnose proper functions at the very early stages, however, this method, like other methods, faces some limitations, including:

The time to do the test, taking the dose of glucose, fasting before the test and waiting time for the body
The results of this test can be affected by conditions such as stress, illness, or drug use.
This test is safe, but there may be some reactions to oral glucose, including nausea and vomiting. If vomiting occurs during the test, the test has not been performed completely.
GTT testing is not recommended under the following conditions:
An individual has already been diagnosed with diabetes.
The person is allergic to sugar or dextrose.
In the recovery period, after surgery, there is damage or infection.
A person has high stress levels under physiological conditions.
A person has already experienced hypocalomic paralysis.
What steps should be taken before testing the OGTT?
Before going to the lab, the person should be fast and at least 8-12 hours long. Drinking a little water will not be a problem if needed. This test should usually be scheduled for the morning. You must have enough time to do the test for 3-4 hours or 2-1 hours. Since stress can affect the results of this test, you should be present at the laboratory for half an hour before testing.

Some medications can affect your blood glucose levels and you may need to discontinue taking them before testing. These medications include:

Anticonvulsants such as tuporomat and valproate
Corticosteroids like prednisolone or medulla
Quinolone antibiotics such as ciprofloxacin or levofloxacin
Statin drugs such as atrostatin and risostatin
Three-ring antidepressants such as clomipramine or imipramine
Salicylic acid medications such as aspirin
Unusual antipsychotics such as clozapine or ketodyapin
After GTT testing
Although some side effects are likely, some people may experience nausea, stomach upset and diarrhea after drinking glucose. To treat diarrhea, you can take anti-diarrhea drugs or ginger tea, chewing gum




Fatemeh Ghorbani

Fatemeh Ghorbani

فاطمه قربانی هستم، لیسانس ژنتیک، به علوم نوین پزشکی و ایمونولوژی علاقمندم. از شما دوست گرامی بخاطر مطالعه این مقاله و همچنین مجموعه تریتا بخاطر فرصت انتشار مطالبم در راستای کمک به ارتقای دانش کمال تشکر دارم. شاد باشید و سلامت

my name is Fatemeh Ghorbani, I have a B.S in genetics and interested in immunology and medical science. I believe that, even into the smallest acts, should be put our heart, mind and soul. Thank you for reading my article