Topic Overview

To be diagnosed with diabetes, you must meet one of the following criteria:^{footnote 1}

• Have symptoms of diabetes (increased thirst, increased urination, and unexplained weight loss) and a blood sugar level equal to or greater than 200 milligrams per deciliter (mg/dL). The blood sugar test is done at any time, without regard for when you last ate (random plasma glucose test or random blood sugar test).
• Have a fasting blood sugar level that is equal to or greater than 126 mg/dL. A fasting blood sugar test (fasting plasma glucose) is done after not eating or drinking anything but water for 8 hours.
• Have a 2-hour oral glucose tolerance test (OGTT) result that is equal to or greater than 200 mg/dL.
• Have a hemoglobin A1c that is 6.5% or higher. This test is most reliable for adults. Some experts recommend using one of the other tests to diagnose diabetes in children. This test may not be appropriate for everyone because many things can affect the life span of red blood cells, such as the second or third trimester of pregnancy, a recent blood loss or a blood transfusion, sickle cell disease, hemodialysis, or erythropoietin (ESA) medicine.

Two tests are used to confirm the diagnosis of diabetes.

If the results of your fasting blood sugar test are between 100 mg/dL and 125 mg/dL, your OGTT result is between 140 to 199 mg/dL (2 hours after the beginning of the test), or your hemoglobin A1c is 5.7% to 6.4%, you have prediabetes. This means that your blood sugar is above normal but not high enough to be diabetes. Discuss with your doctor how often you need to be tested.

There are different types of diabetes. Sometimes it’s hard to diagnose the type of diabetes you have because the symptoms are different or the normal treatments don’t work well. Your doctor may do a C-peptide test or test for autoantibodies. These tests can help diagnose type 1 diabetes or a slowly developing form of type 1 diabetes called latent autoimmune diabetes in adults (LADA). Another form of diabetes, maturity onset diabetes of the young (MODY), is an inherited disease caused by a change (mutation) in a gene. There are many types of MODY depending on the gene that is affected. Genetic testing can help you and your doctor decide how to treat MODY.