Tests to Diagnose Diabetes

One test to diagnose diabetes is called a fasting glucose test. A blood sample is taken before breakfast, after a 10- to12-hour fast. A normal fasting result is less than 110 mg/dl. If the blood glucose value is above 126 mg/dl more than once, the person has diabetes.

The oral glucose tolerance test is also used to diagnose diabetes. After a 10- to12-hour fast, a blood sample is taken. A glucose dose is given and blood samples are taken every 30 minutes. If the test after two hours is equal to or greater than 200 mg/dl, the person has diabetes.

A casual plasma glucose, or a random blood glucose of greater than 200 mg/dl, with symptoms, also indicates the person has diabetes.