Diabetes 101: Fasting Blood and Glucose Tolerance Tests

A fasting blood test is a blood test that requires you to fast. A glucose tolerance test is a test that checks how your body reacts to sugar. These two tests play very important roles in patients with diabetes.

Fasting blood and glucose tolerance tests are “bywords” for diabetics. A fasting blood test is simply a blood test done to you after not taking anything. Normal blood test does not require anything to do before the tests, but fasting blood test requires you not to eat and drink before the test so that the results are not affected by your intake.

Fasting blood glucose test

Fasting blood glucose test is a blood test that requires the subject not to eat nor drink 8 to 10 hours before the test. This is used to detect diabetes, an illness where sugar amounts in the blood.

Blood glucose test is also used to determine high blood sugar or hyperglycemia and low blood sugar or hypoglycemia. Fasting blood test, together with glucose tolerance test helps monitor levels of sugar or glucose in blood for patients who already have diabetes.

Glucose in the blood can be measured depending on its purpose, such as random testing or anytime; on a fasting basis, a test is usually done after not eating or drinking anything after 8-10 hours; as part of a glucose tolerance test or oral glucose challenge (OGTT/GTT); and post prandial, which is after a meal.

Glucose tolerance test

The glucose tolerance test is done to see how the body metabolizes sugar, most common of which is the Oral Glucose Tolerance Test or OGTT. This requires not eating or drinking anything after midnight prior to the test.

While fasting blood test determines the level of sugar in the blood, glucose tolerance test determines how your body reacts to sugar. During this latter test, which lasts for about three hours, your blood will be taken; then you shall be required to take a glucose-containing liquid and after 30 to 60 minutes, your blood shall be taken again.

The way of the Intravenous Glucose Tolerance Test or IGTT is they measure your blood glucose, then they inject glucose to your veins for three minutes and after one to three minutes, measure your blood glucose again. Timing though may vary.