G.T.T. is necessary in uncontrolled diabetes. G.T.T. will reveal the low and high peaks of rise and fall in glucose levels. It will also point to the time of absorption and release of glucose by the system. It is considered to be the most accurate test which reveals a clear diabetic status of a patient.

First, samples of blood and urine are taken on empty stomach. Thereafter, 1gm of glucose is given per kg body weight, then after half an hour (upto two hours and in certain cases even upto three hours) blood and urine samples are taken and the respective readings are noted down. But, W.H.O.studies have recommended that only one test, (two hours after taking glucose) will suffice to know the exact position and status of a person. They consider this to be the most accurate method.