The glucose tolerance test is the best way to know if you are prediabetic. It is used to diagnose type 2 diabetes, the existence of borderline diabetes (prediabetes), and gestational diabetes during pregnancy.
It is also called the GTT or OGTT (the O is for oral).
This test will detect hyperglycemia (too much sugar in the blood), but it cannot diagnose hypoglycemia (too little sugar in the blood) even if your fasting blood sugar is unusually low.
Your doctor cannot tell you that you have chronic hypoglycemia from a single blood test, unfortunately.
But he can use the GTT to prove that you are becoming sensitive to glucose from insulin resistance, the symptom of prediabetes.
It is very important to eat your normal diet in the days before the test and to keep your activity level the same, too.
If you eat an unusually large meal the day before the test or do not stick to your regular eating routine, the GTT results will be inaccurate.
Illness and infections mess up the test too. Also, you need to let your doctor know all the medications you are on because they may affect the results.
Other things that can make your GTT test a false positive for diabetes are stress, trauma, heart attack and stroke. Anything that involves your pancreas, such as pancreatitis, will change your results.
This is why the American Diabetic Association recommends doctors do the glucose tolerance test twice to be sure it is accurate.
Your doctor will tell you to fast the night before the test and skip breakfast. You need to be without food for at least 8 hours before the test begins.
At your doctor visit, the nurse will give you a fingerstick blood test, which might hurt for a second. The glucose monitor number will be recorded.
Then you will be given an 8-ounce cup of syrupy liquid which you must drink within a 5-minute window.
You will wait for an hour, and then they give you another fingerstick blood test. After a second hour of waiting comes a third fingerstick test.
Some doctors continue for a third hour and do another blood test, but the 2-hour number on the glucose tolerance test will tell them what they need to know.
A normal fasting blood sugar should be below 110. If it is between 110 and 125 you are considered a borderline or prediabetic.
A fasting number above 125 will give you a working diagnosis of diabetes, and the reaction to the glucose you drank will show in the high numbers at the 2-hour test, confirming the diagnosis.
If your fasting number is normal, and if after 2 hours your blood sugar has dropped below 140 you do not have insulin resistance.
But if the number is between 140 and 200, you have impaired glucose tolerance. That means insulin resistance or prediabetes.
For a woman it may also mean you have polycystic ovarian syndrome, which presents as prediabetes with elevated blood sugar. It's a good idea to ask an endocrinologist to rule this out for you.
If you are pregnant, the blood sugar ranges for gestational diabetes are a little different, and the test might only take one hour instead of two or three.
If you do have gestational diabetes, your doctor will monitor your blood sugar carefully over the rest of your pregnancy.
You will be encouraged to watch your diet and keep weight gain to a minimum. Most of the time blood sugars return to normal after delivery.
However, be aware that both polycystic ovarian syndrome and gestational diabetes put you at risk for type 2 diabetes later in your life, so keep getting blood sugar testing over time. You do not want diabetes to sneak up on you.
If the fingerstick test two hours after taking the glucose drink is above 200, most people receive a diagnosis of diabetes.
Your doctor may ask for another oral glucose tolerance test to verify the diagnosis, especially if there are other things going on that make him suspect the test is not accurate, or if it is barely above or below 200.
If you have a normal body mass index (BMI), normal triglyceride levels and are obviously not overweight, it's time to talk to your doctor about the possibility of latent adult onset type 1 diabetes (LADA).Here is more information about LADA and how to get tested for it.
If you are prediabetic you will be given suggestions for things to do to lower your blood sugar, such as limiting sugary and processed carbohydrates (diabetic AGEs).
You'll be encouraged to exercise more and lose weight. (Here are a few weight loss secrets). Even small changes will make a difference in the numbers.
If your glucose tolerance test shows type 2 diabetes, most doctors start you right away on diabetic medication, before you have begun trying diet and exercise.
But by following the results of type 2 diabetics who are encouraged to exercise and get educated about a diabetic diet, researchers find that about half of them do not need medications to control their condition.
So why are doctors in such a hurry to start medications? Maybe they realize that most of us are not ready to change lifetime habits.
Besides, if we have extremely high blood sugar numbers or serious diabetic complications, we need swift intervention to bring those blood sugars down.
I had become diabetic without knowing it and was
diagnosed after a small stroke. This is why medications were started
right away. It took several years for me to come to grips with the changes I needed to make.
If you are at risk, please get tested without delay. The glucose tolerance test remains a reliable first diagnostic tool for smoking out prediabetes.
It gives you a chance to start those lifestyle changes before you become diabetic. This knowledge is a great gift if you choose to do something about it.
[Go back to the top]