Your health care professional can diagnose diabetes, prediabetes, and gestational diabetesthrough 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 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 Trial Net 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 factor
- Are a woman who had gestational diabetes
Gestational diabetes
All pregnant women who do not have a prior diabetes diagnosis should be tested for gestational diabetes. If you are pregnant, you will take a glucose challenge test between 24 and 28 weeks of pregnancy.
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 haemoglobin A1C, HbA1C, glycated haemoglobin, and glycosylated haemoglobin 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 anaemia or another problem with your blood.1 The A1C test is not accurate in people with anaemia.
If you’re of African, Mediterranean, or Southeast Asian descent, your A1C test results may be falsely high or low. Your health care professional may need to order a different type of A1C test.
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.
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.