Related tests: Complete urinalysis, A1C, Insulin, C-peptide, Microalbuminuria
Clinical significance
The glucose tolerance curve (OGTT, oral glucose tolerance test) measures the blood glucose concentration before and after a set amount of glucose is taken by mouth: normally the body responds to the rapid rise in blood glucose by releasing insulin, which stops glucose from exceeding, at the set time, the threshold for the amount given; exceeding the threshold indicates impaired glucose tolerance (IGT), i.e. an early relative lack of insulin that could progress to diabetes.
The OGTT is typically requested when fasting blood glucose is between 110 and 126 mg/dL (see glucose) or in pregnant women (especially if overweight). The standard dose of glucose is 75 g, and the second blood sample is taken after 120 minutes. In pregnant women at the first visit the dose is 50 g and the second sample is taken after 60 minutes (the so-called mini-curve); if the result is abnormal, the test is repeated with 75 g and 3 samples are taken: baseline, 60 and 120 minutes.
Clinical indications
Distinguishing between IGT and IFG
Sample type
The patient must have a blood sample taken.
Preparation
Fast for at least 8 hours. Only water is allowed. After the first (baseline) sample, you must remain seated, without eating, drinking or smoking, until the following samples have been taken.