Oral Glucose Tolerance Test

The oral glucose tolerance test (OGTT) measures the body's ability to use a type of sugar, called glucose, that is the body's main source of energy. An OGTT can be used to diagnose prediabetes and diabetes. An OGTT is most commonly done to check for diabetes that occurs with pregnancy (gestational diabetes).

Glucose intolerance is a mild form of pre-diabetes in which pregnant women have slightly higher blood sugar levels than normal on the Oral Glucose Tolerance Test (OCT), a standard prenatal test usually given to women toward the end of their second trimester. Results indicating gestational glucose intolerance aren't usually considered as serious as if the mother has gestational diabetes, since glucose intolerance is fairly mild and can be controlled through diet

Why It Is Done
The oral glucose tolerance test (OGTT) is done to:

Check pregnant women for gestational diabetes. When done for this purpose, the test is called a glucose challenge screening test, and it is usually done during the 24th to the 28th week of pregnancy. You have an increased chance of developing gestational diabetes if you:
Have had gestational diabetes during a previous pregnancy.
Have previously given birth to a baby who weighed more than 8.8lb.
Are younger than age 25 and were overweight before getting pregnant.
Confirm the presence of gestational diabetes if other blood glucose measurements are high.
Screen women who have polycystic ovary syndrome (PCOS) for diabetes.
Diagnose prediabetes and diabetes.

Glucose tolerance diagnostic test
To prepare for the glucose tolerance diagnostic test:

Eat a balanced diet that contains at least 150 to 200 grams (g) of carbohydrate per day for 3 days before the test. Fruits, breads, cereals, grains, rice, crackers, and starchy vegetables such as potatoes, beans, and corn are good sources of carbohydrate.
Do not eat, drink, smoke, or exercise strenuously for at least 8 hours before your first blood sample is taken.
Tell your health professional about all prescription and nonprescription medicines you are taking. You may be instructed to stop taking certain medicines before the test.
The glucose tolerance diagnostic test may take up to 4 hours. Since activity can interfere with test results, you will be asked to sit quietly during the entire test. Do not eat during the test. You may drink only water during this time.

Output study show that GTF and insulin act synergistically.

The acute metabolic effects of glucose tolerance factor (GTF), the biologically active form of trivalent chromium, were studied in normal and genetically diabetic (db/db) mice. A single intraperitoneal injection of GTF significantly reduced the nonfasting plasma glucose level in normal mice by 38 per cent, and in diabetic mice by 14 to 29 per cent.

Time course studies in normal and diabetic mice showed a maximal lowering of plasma glucose at four hours after GTF treatment. Furthermore, a single injection of GTF significantly lowered the elevated plasma triglyceride and cholesterol levels by 47 and 35 per cent, respectively, four hours after injection.

Genetically diabetic mice are refractory to insulin, and treatment with exogenous insulin produced a smaller decrement in plasma glucose (11-18 per cent). The combination treatment of diabetic mice with GTF and exogenous insulin was significantly more effective in reducing plasma glucose (39-51 per cent) and triglycerides (76 per cent) than either treatment alone.

These findings are consistent with the suggestion that GTF and insulin act synergistically.