Do I Need an Oral Glucose Tolerance Test?

Your blood sugar level can give your doctor important clues about your health, and an oral glucose tolerance test (OGTT) shows how well your body handles sugar from foods.

It can tell whether you are at risk for diabetes or if you already have it. A shorter version of an OGTT checks for diabetes during pregnancy.

Normally when you eat, your blood sugar rises. Your pancreas, a long gland deep in the belly, releases a hormone called insulin. It helps move sugar from your blood into your cells for energy and storage. Then your blood sugar goes back down to normal.

If you have type 2 diabetes, your body uses insulin poorly. Glucose builds up in your blood. This excess sugar can damage blood vessels around your body. Diabetes can lead to heart disease, nerve damage, eye disease, and kidney damage.

When Do I Need the Test?

You might need an oral glucose tolerance test if you:

A shorter version of this test is done between the 24th and 28th week of pregnancy to see whether you have gestational diabetes. It's called the oral glucose challenge test.

How Do I Get Ready?

To get an accurate result on the OGTT, eat about 150 grams of carbohydrates each day for 3 days before the test. Don't eat or drink anything except water after about 10 o’clock the night before.

You don't need to do any special prep before the pregnancy glucose challenge test. You can eat in the morning. Just avoid foods with a lot of sugar, such as doughnuts or orange juice.

How Is It Done?

You'll get the OGTT at your doctor's office, a clinic, hospital, or lab. Here’s what happens:

  • A nurse or doctor will take a blood sample from a vein in your arm to test your starting blood sugar level.
  • You'll then drink a mixture of glucose dissolved in water.
  • You'll get another blood glucose test 2 hours later.

During pregnancy, the test is shorter. You'll drink a sweet liquid. Then you'll have a blood test about 60 minutes later.

Continued

Any Problems from Taking It?

The OGTT has very few issues. Some people have minor side effects from the sugary drink or from the needle stick.

Side effects from the drink include:

Possible problems from the blood test include:

  • Excess bleeding
  • Fainting
  • Infection
  • More than one attempt to find a vein, which can hurt a little

What Do the Results Mean?

Your blood glucose level should rise after you finish the sugary drink. Then it should go back to normal, as insulin moves glucose into your cells. If your blood sugar takes a long time to go back to normal, you could have diabetes.

You might see a measurement from the test written out as “mg/dL.” It stands for milligrams per deciliter. Two hours after you finish the glucose drink, this is what your results mean:

Below 140 mg/dL: normal blood sugar

Between 140 and 199: impaired glucose tolerance, or prediabetes

200 or higher: diabetes

When you're pregnant, a blood glucose level of 140 mg/dL or higher is abnormal. Your doctor will recommend that you take a 3-hour OGTT. During this longer test, you'll have blood drawn before you drink a sugary solution. Then you'll have your blood tested every hour for three hours.

What Happens Next?

If you have prediabetes, your doctor will talk to you about ways to stop it from turning into a full-blown case. Exercise and weight loss are two ways to lower your risk for type 2 diabetes.

If the test shows you have diabetes, you might get what’s called an “A1C” or other tests to confirm the diagnosis. Diet, exercise, and medicine can help control your blood sugar.

Good foods and physical activity can also help control diabetes during pregnancy. Your blood sugar should go back to normal after your baby is born.

But gestational diabetes increases your risk of getting type 2 diabetes after your pregnancy. You'll need to stay on a healthy diet and exercise plan to avoid a future diabetes diagnosis.

WebMD Medical Reference Reviewed by Laura J. Martin, MD on September 17, 2016

Sources

SOURCES:
 

American Academy of Family Physicians: "Diabetes."

American Association for Clinical Chemistry: "Glucose Tests."

American Diabetes Association: "Diagnosing Diabetes and Learning About Prediabetes," "How to Treat Gestational Diabetes."

CDC: "Oral Glucose Tolerance Test (OGTT) Procedures Manual."

Cleveland Clinic: "Oral glucose tolerance test during pregnancy."

Dartmouth-Hitchcock: "Oral Glucose Tolerance Test."

National Institute of Diabetes and Digestive and Kidney Diseases: "Step 1: Learn About Diabetes."

PubMed Health: "Glucose tolerance tests: What exactly do they involve?"

St. Joseph-Mercy Hospital: "Preparing for the Oral Glucose Tolerance Test (Adults)."

Mayo Clinic, “Glucose tolerance test,” “Triglycerides, why do they matter?” Polycystic ovary syndrome (PCOS).

Johns Hopkins Medicine, “What is the pancreas?”

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