What Tests to Expect

Why is screening for diabetes important?

People can have prediabetes or type 2 diabetes for years and not have any obvious signs or symptoms. Type 2 diabetes is often not diagnosed until health problems appear as a result of high blood glucose. These can include vision problems, kidney disease, or nerve damage. If left untreated, diabetes can cause more serious problems like blindness, kidney failure, leg amputation, heart attacks, and stroke.

It’s important to know if you have prediabetes or diabetes, so you can make lifestyle changes or take medication to manage your condition. People at risk should be screened (tested) for diabetes and prediabetes.

How do you get screened for diabetes?

There are three blood tests that can be used to check the levels of glucose in your blood and diagnose prediabetes or diabetes:

  • Fasting blood glucose test (FBG). Blood is drawn in the morning after you go without food overnight or for at least 8 hours.
  • Oral glucose tolerance test (OGTT). This test is also done in the morning after going without food overnight or for at least 8 hours. Blood is drawn before you drink 8 ounces of a sugar solution and 2 hours after. This test is more precise but less convenient than the FBG test.
  • Hemoglobin A1C test (A1C).This test shows what your average blood glucose levels have been over the past 2–3 months. You can eat and drink normally before the test.

What is an A1C test?

The A1C test is a blood test used to diagnose diabetes and to aid in its management. Current guidelines recommend an A1C level below 7% in healthy adults and below 7.5% in children with certain medical conditions. The A1C target may differ between individuals based on age, medical conditions, and other factors. The test measures your average blood glucose over the past two to three months and shows how well your treatment plan is working overall. It does not take the place of daily blood glucose measurements, which show the level of glucose in your blood at that moment. Blood glucose levels change throughout the day depending on what and when you eat, whether or not you exercise, and which medications you may be taking. Blood glucose can be measured using a blood glucose meter or continuous glucose monitor (CGM), which measures glucose levels in the fluid between body cells every few minutes throughout the day and night.

When there is too much glucose in the blood, the extra glucose enters red blood cells and attaches to hemoglobin—a protein that carries oxygen to the cells of the body—creating glycated hemoglobin. The A1C test works by measuring the percentage of glucose attached to hemoglobin in the blood. A higher A1C indicates that you should do your best to bring your blood glucose as close to your target to reduce the risk of developing diabetes complications. This may mean changing your medication regimen or diet.

What should your A1C level be?

Most people with diabetes should keep their A1C result below 7% (about 150 mg/dL or less). Studies have shown that people who keep their A1C below 7% greatly reduce their risks of developing long-term complications of diabetes. An average A1C for a person without diabetes is 4–6% Experts recommend that you have your A1C measured at least twice a year.

If Your A1C is Around: Then Your Daily Average Blood Glucose is: (in ml/dL)
12% 298
11% 269
10% 240
9% 212
8% 183
Target area for people with diabetes  
7% 154
6% 126
5% 97

What can I do?

Whether or not you need diabetes medications or insulin, adopting a healthy lifestyle that includes eating well, losing weight if needed, exercising, limiting alcoholic beverages, and not smoking will help you better manage your diabetes.

Source: Diabetes Care 31:1473-1478, 2008

Questions to ask your doctor

  • What was my latest A1C result?
  • What does the result mean?
  • What can I do to keep my blood glucose level on target?
  • How often should I get the A1C test?
  • Should I see a diabetes educator?
  • Should I see an endocrinologist for my care?

←More about Types of Diabetes

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