Overview

Doctors use blood tests and follow guidelines from experts to diagnose diabetes.^{footnote 1}

Criteria for diabetes

You will be diagnosed with diabetes if you meet one of the following criteria:

• You have symptoms of diabetes and a blood sugar level equal to or greater than 11.1 mmol/L.
  • Symptoms include increased thirst, increased urination, and unexplained weight loss.
  • A random blood sugar (plasma glucose) test can be done at any time. It doesn't matter when you last ate.
• Your fasting blood sugar level is equal to or greater than 7.0 mmol/L.
  • A fasting blood sugar (plasma glucose) test is done after you don't eat or drink anything but water for 8 hours.
• Your 2-hour oral glucose tolerance test result is equal to or greater than 11.1 mmol/L.
  • An oral glucose tolerance test (OGTT) is most often done to check for gestational diabetes.
• Your hemoglobin A1c result is 6.5% or higher.
  • The hemoglobin A1c test is most reliable for adults. Some experts recommend using one of the other tests to diagnose diabetes in children.^{footnote 2} This test may not be right for everyone. That's because many things can affect the lifespan 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.

Criteria for prediabetes

You may be diagnosed with prediabetes if your blood sugar is above normal but not high enough to be diabetes. You have prediabetes if you meet one of the following criteria:^{footnote 1}

• Your fasting blood sugar test results are between 6.1 mmol/L and 6.9 mmol/L.
• Your OGTT result is between 7.8 mmol/L and 11.0 mmol/L (2 hours after you start the test).
• Your hemoglobin A1c result is 6.0% to 6.4%.

Ask your doctor how often you need to be tested.

Other possible tests

It may be hard to tell what type of diabetes you have. If so, your doctor may do a C-peptide test or test for autoantibodies to diagnose type 1 diabetes or a slowly developing form of type 1 diabetes called latent autoimmune diabetes in adults (LADA). Some rare forms of diabetes are caused by a genetic problem. You may need genetic testing to diagnose them. This includes maturity onset diabetes of the young (MODY). There are many types of MODY, depending on the gene that is affected.