Results of the oral glucose tolerance test are given in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).
Type 2 diabetes
If you're being tested for type 2 diabetes, two hours after drinking the glucose solution:
- A normal blood glucose level is lower than 140 mg/dL (7.8 mmol/L).
- A blood glucose level between 140 mg/dL and 199 mg/dL (7.8 and 11 mmol/L) is considered impaired glucose tolerance, or prediabetes. If you have prediabetes, you're at risk of eventually developing type 2 diabetes. You're also at risk of developing heart disease, even if you don't develop diabetes.
- A blood glucose level of 200 mg/dL (11.1 mmol/L) or higher may indicate diabetes.
If the results of your glucose tolerance test indicate type 2 diabetes, your doctor may repeat the test on another day or use another blood test to confirm the diagnosis. Various factors can affect the accuracy of the glucose tolerance test, including illness, activity level and certain medications.
If you're being tested for gestational diabetes, your doctor will consider the results of each blood glucose test.
At Mayo Clinic, if your blood glucose level is higher than 140 mg/dL (7.8 mmol/L) after the one-hour test, your doctor will recommend the three-hour test. If your blood glucose level is higher than 190 mg/dL (10.6 mmol/L) after the one-hour test, you'll be diagnosed with gestational diabetes.
For the three-hour test:
- A normal fasting blood glucose level is lower than 95 mg/dL (5.3 mmol/L).
- One hour after drinking the glucose solution, a normal blood glucose level is lower than 180 mg/dL (10 mmol/L).
- Two hours after drinking the glucose solution, a normal blood glucose level is lower than 155 mg/dL (8.6 mmol/L).
- Three hours after drinking the glucose solution, a normal blood glucose level is lower than 140 mg/dL (7.8 mmol/L).
If one of the tests is higher than normal, you'll likely need to test again in four weeks. If two or more of the tests are higher than normal, you'll be diagnosed with gestational diabetes.
If you're diagnosed with gestational diabetes, you can prevent complications by carefully managing your blood glucose level throughout the rest of your pregnancy.
March 12, 2015
- American Diabetes Association. Classification and diagnosis of diabetes. Diabetes Care. 2015;38(suppl):S8.
- Diagnosing diabetes and learning about prediabetes. American Diabetes Association. http://www.diabetes.org/diabetes-basics/diagnosis. Accessed Jan. 27, 2015.
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- American College of Obstetricians and Gynecologists (ACOG) Committee on Practice Bulletin – Obstetrics. ACOG Practice Bulletin No. 137. Gestational diabetes mellitus. Obstetrics and Gynecology. 2013;122:406.
- Coustan DR, et al. Diabetes mellitus in pregnancy: Screening and diagnosis. http://www.uptodate.com/home. Accessed Jan. 27, 2015.
- AskMayoExpert. What tests are needed to confirm the diagnosis of gestational diabetes mellitus during pregnancy? Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2014.