How is Diabetes Diagnosed?

There are several ways to diagnose diabetes. Each method usually requires that your tests be done twice to ensure that you have diabetes. If your doctor determines that your blood glucose level is very high, or if you have symptoms of high blood glucose and your glucose test is high, you may not need to have a second test to diagnose diabetes.

Testing should be carried out in a health care setting (such as a doctor’s office or lab). Tests to diagnose diabetes include:

A1C: The A1C test measures your average blood glucose for the past two to three months. This is a blood test so you will not have to fast or drink anything. Diabetes is diagnosed if the A1C is 6.5% or higher.

Fasting Plasma Glucose (FPG): This is a blood test that checks your fasting blood glucose levels. For this test, you must fast, that is not having anything to eat or drink (except water) for at least 8 hours before the test. This test is usually done first thing in the morning, before breakfast. Diabetes is diagnosed if fasting blood glucose is 126 mg/dL or higher.

Oral Glucose Tolerance Test (OGTT): The OGTT is a two-hour test that checks your blood glucose levels before, and again two hours after, you drink a special sweet drink. It tells the doctor how your body processes glucose. Diabetes is diagnosed if the two hour blood glucose test is 200 mg/dL or higher.

Random (also called Casual) Plasma Glucose Test. This test is a blood check done at any time of the day when you have severe diabetes symptoms. Diabetes is diagnosed if blood glucose is 200 mg/dL or higher.

How is Prediabetes Diagnosed?

Prediabetes is a condition where your blood glucose is higher than normal but not high enough to be diabetes. This condition puts you at risk for developing type 2 diabetes.

There are no clear symptoms of prediabetes, so it is possible to have it and not know it. Some people with prediabetes may have some symptoms of diabetes or problems associated with it. People usually find out that they have prediabetes during diabetes testing. If you have prediabetes, you should be checked for type 2 diabetes every one to two years.

Prediabetes is diagnosed if:

  • A1C is 5.7% – 6.4%.
  • Fasting blood glucose is 100 – 125 mg/dL.
  • OGTT two-hour blood glucose is 140 mg/dL – 199 mg/dL.