GLUCOSE TOLERANCE TEST (GTT)

Glucose tolerance test (GTT)

It is a blood test that is used to assess how well your body tolerates glucose. . Food that is eaten is broken down into simple Carbohydrates which is taken up the body cells with help of insulin (type of hormone) secreted by the pancreas.

Whenever there is decrease production of insulin or increase resistance of cells to action of insulin, it causes increase in blood levels of glucose. these high levels of blood glucose is known as diabetes/prediabetes. This condition is risky as it may cause damage to various organs of the body like heart, kidneys, intestine, eyes etc.

Why is GTT (glucose tolerance test) prescribed?

Your health care provider may ask to undergo glucose tolerance test in following conditions:

• Diagnosis of diabetes and prediabetes
• Screen for diabetes and prediabetes
• Screen for Gestational Diabetes

What are the components of glucose tolerance test?

This is an oral glucose tolerance test in which glucose levels in the blood are tested after giving glucose orally. The readings of test are taken at fasting, 1 hr, 2 hr and 3 hr after taking glucose powder orally.

Procedure and prerequisites

This is a little prolonged test in which multiple samples of blood are taken at regular intervals. You are asked to fast for at least 8 hrs or preferably overnight for the test. You can drink plain water if you want.

On the day of test the lab technician will first take a fasting blood sample. After that you are asked to drink water containing specific amount of glucose. the amount of glucose is usually 75gms or 100 gms depending on the treating doctor. After that blood samples are drawn at regular intervals for next 3 hrs (every hour). you are required not to eat or drink anything during this time, except water.

Reference range

Normal values-taken after giving 75 Gms glucose in adults excluding pregnancy-

Response	Fasting (mg/dl)	2 hrs Post 75 g load (mg/dl)
Normal Response	70-100	70-140
Impaired Fasting Glucose	101-125	70-140
Impaired Glucose Tolerance	70-100	141-199
Pre Diabetes	>=126	>=200