Diabetes Tests & Diagnosis

Your health care professional can diagnose diabetes, prediabetes, and gestational diabetes through blood tests. The blood tests show if your blood glucose, also called blood sugar, is too high.

Do not try to diagnose yourself if you think you might have diabetes. Testing equipment that you can buy over the counter, such as a blood glucose meter, cannot diagnose diabetes.

Who should be tested for diabetes?

Anyone who has symptoms of diabetes should be tested for the disease. Some people will not have any symptoms but may have risk factors for diabetes and need to be tested. Testing allows health care professionals to find diabetes sooner and work with their patients to manage diabetes and prevent complications.

Testing also allows health care professionals to find prediabetes. Making lifestyle changes to lose a modest amount of weight if you are overweight may help you delay or prevent type 2 diabetes.

Type 1 diabetes

Most often, testing for type 1 diabetes occurs in people with diabetes symptoms. Doctors usually diagnose type 1 diabetes in children and young adults. Because type 1 diabetes can run in families, a study called TrialNet offers free testing to family members of people with the disease, even if they don’t have symptoms.

Type 2 diabetes

Experts recommend routine testing for type 2 diabetes if you

•are age 45 or older

•are between the ages of 19 and 44, are overweight or obese, and have one or more other diabetes risk factors

•are a woman who had gestational diabetes¹

Medicare covers the cost of diabetes tests for people with certain risk factors for diabetes. If you have Medicare, find out if you qualify for coverage. If you have different insurance, ask your insurance company if it covers diabetes tests.

Though type 2 diabetes most often develops in adults, children also can develop type 2 diabetes. Experts recommend testing children between the ages of 10 and 18 who are overweight or obese and have at least two other risk factors for developing diabetes.¹

•low birthweight

•a mother who had diabetes while pregnant with them

•any risk factor mentioned in Risk Factors for Type 2 Diabetes

What tests are used to diagnose diabetes and prediabetes?

Health care professionals most often use the fasting plasma glucose (FPG) test or the A1C test to diagnose diabetes. In some cases, they may use a random plasma glucose (RPG) test.

Fasting plasma glucose (FPG) test

The FPG blood test measures your blood glucose level at a single point in time. For the most reliable results, it is best to have this test in the morning, after you fast for at least 8 hours. Fasting means having nothing to eat or drink except sips of water.

A1C test

The A1C test is a blood test that provides your average levels of blood glucose over the past 3 months. Other names for the A1C test are hemoglobin A1C, HbA1C, glycated hemoglobin, and glycosylated hemoglobin test. You can eat and drink before this test. When it comes to using the A1C to diagnose diabetes, your doctor will consider factors such as your age and whether you have anemia or another problem with your blood.¹ The A1C test is not accurate in people with anemia.

Your health care professional will report your A1C test result as a percentage, such as an A1C of 7 percent. The higher the percentage, the higher your average blood glucose levels.

People with diabetes also use information from the A1C test to help manage their diabetes.

Random plasma glucose (RPG) test

Sometimes health care professionals use the RPG test to diagnose diabetes when diabetes symptoms are present and they do not want to wait until you have fasted. You do not need to fast overnight for the RPG test. You may have this blood test at any time.

What test numbers tell me if I have diabetes or prediabetes?

Each test to detect diabetes and prediabetes uses a different measurement. Usually, the same test method needs to be repeated on a second day to diagnose diabetes. Your doctor may also use a second test method to confirm that you have diabetes.

The following table helps you understand what your test numbers mean.

Which tests help my health care professional know what kind of diabetes I have?

Even though the tests described here can confirm that you have diabetes, they can’t identify what type you have. Sometimes health care professionals are unsure if diabetes is type 1 or type 2. A rare type of diabetes that can occur in babies, called monogenic diabetes, can also be mistaken for type 1 diabetes. Treatment depends on the type of diabetes, so knowing which type you have is important.

To find out if your diabetes is type 1, your health care professional may look for certain autoantibodies. Autoantibodies are antibodies that mistakenly attack your healthy tissues and cells. The presence of one or more of several types of autoantibodies specific to diabetes is common in type 1 diabetes, but not in type 2 or monogenic diabetes. A health care professional will have to draw your blood for this test.

If you had diabetes while you were pregnant, you should get tested 6 to 12 weeks after your baby is born to see if you have type 2 diabetes.