Key takeaways

  • Type 2 diabetes is often diagnosed using blood tests, such as the A1C, fasting plasma glucose, random plasma glucose, and oral glucose tolerance test. A diagnosis typically requires two positive tests.
  • The A1C test measures average blood sugar over 2 to 3 months and doesn’t require fasting, while the fasting plasma glucose test requires fasting for at least 8 hours before measuring blood sugar levels.
  • Early diagnosis and management of type 2 diabetes are crucial for preventing severe complications. Individuals over 45 or with risk factors should discuss testing with their doctor.

Diabetes is a long-term (chronic) condition that happens when your body doesn’t produce enough insulin, or can’t use insulin well. As a result, your blood sugar can become too high, which can lead to serious health problems over time.

The good news is that type 2 diabetesisa manageable condition. Once you’re diagnosed, you can work with your doctor to develop a treatment plan to stay healthy. Early diagnosis and management is important to help prevent serious outcomes.

While diabetes can usually be managed well, it’s important to take your treatment plan seriously. According to the CDC, diabetes is the 7th leading cause of death in the United States.

Many of the severe complications of diabetes can be avoided with treatment. That’s why an early diagnosis is so important.

The symptoms of type 2 diabetes often develop gradually. Because you may or may not have symptoms, your doctor will use blood tests to confirm your diagnosis.

These blood tests can be used to measure the amount of sugar (glucose) in your blood:

  • A1C (glycated hemoglobin) test
  • fasting plasma glucose test
  • random plasma glucose test
  • oral glucose tolerance test

We’ll look at each of these tests in more detail later in the article.

Your doctor will request one or more blood tests to confirm your diagnosis. A test will usually be completed more than once to confirm the result, unless you have clear symptoms of diabetes.

What to expect during blood sugar testing

To do a blood test, a lab technician, nurse, or other healthcare professional will use a small needle to draw a sample of your blood. The sample is then sent to a lab for testing.

Some diabetes tests require you to prepare for the test. For example, you may be asked to fast (avoid eating and drinking) for a set period of time before the test. Your doctor will give you instructions to tell you how to prepare for your tests.

Next, let’s take a closer look at some blood tests commonly used to diagnose diabetes.

What is A1C?

The A1C test measures your average blood sugar level over the past 2 to 3 months. It’s sometimes called the glycated hemoglobin test.

This test measures the amount of glucose (sugar) attached to the hemoglobin in your blood. Hemoglobin is the oxygen-carrying protein in your red blood cells. The higher your A1C, the higher your recent blood sugar levels have been.

An advantage of the A1C test is convenience. You don’t have to fast before this test. And the blood sample can be collected at any time of day.

Here’s what your A1C test results could mean:

A1CResult
Below 5.7%Normal
5.7 to 6.4%Prediabetes
6.5% or higherDiabetes

A1C testing is also used to monitor your blood sugar management after you’ve been diagnosed with diabetes. If you have diabetes, your A1C levels should be checked at least twice a year.

Factors that can affect A1C results

A1C measures sugar that’s attached to hemoglobin in your blood. One type of hemoglobin, hemoglobin A, is the most common. But there are many more types of hemoglobin, known as hemoglobin variants. In some cases, having a hemoglobin variant can affect your A1C results.

About 7 percent of people around the world are born with hemoglobin variants, and most people don’t know they have it. Some hemoglobin variants are more common in people of African, Mediterranean, or Asian heritage.

Having a hemoglobin variant can cause your A1C test result to be incorrectly high or low. If your doctor finds that your A1C results don’t seem to be consistent with your symptoms or your other test results, they will likely ask for additional tests.

Some health conditions such as anemia, kidney disease, and liver failure can also affect A1C results. Don’t worry — your doctor will repeat the tests before making a diagnosis. Other tests can also be used besides A1C that would be more accurate in these cases.

The fasting plasma glucose test measures your blood sugar at the time of the test. This is different from the A1C test, which measures blood sugar levels over a longer period of time.

For the fasting plasma glucose test, a sample of your blood will be taken after you’ve fasted for at least 8 hours, usually overnight. This means that you have consumed no food or drinks during that time. Your doctor will tell you if you can sip water while fasting before the test.

Your test results will usually be expressed in milligrams per deciliter (mg/dL).

Here’s what your results could mean:

Fasting plasma glucoseResult
up to 99 mg/dLNormal
100 to 125 mg/dLPrediabetes
126 mg/dL or higherDiabetes

Random blood sugar testing is usually used for people who have symptoms of diabetes. A random blood sugar test can be done at any time of day. You do not need to fast before this test.

No matter when you last ate, a random blood sugar test of 200 mg/dL or above suggests that you may have diabetes. This is particularly true if you already have symptoms of diabetes.

The oral glucose tolerance test (OGTT) measures your blood sugar before and after you drink a sugary liquid that’s specially formulated for the test. Like the fasting plasma glucose test, you’ll be required to fast overnight beforehand.

When you arrive at your appointment, you’ll first undergo a fasting blood sugar test. Then you’ll drink the sugary liquid. After you’re done, your doctor will test your blood sugar levels periodically for several hours.

This test detects diabetes better than other tests, such as the fasting plasma glucose test. But it’s more costly and takes longer than other blood sugar tests.

For an oral glucose tolerance test, here’s what your results could mean:

Oral glucose toleranceResult
up to 140 mg/dLNormal
140 to 199 mg/dLPrediabetes
200 mg/dL or higherDiabetes

A different version of this test is used to diagnose gestational diabetes. The numbers your doctor will use to make a diagnosis are also different.

Initially, your test results may vary. For instance, a fasting plasma glucose test may show that you have diabetes but an A1C test may show that you don’t. The reverse can also be true.

How does this happen? It could mean that you’re in an early stage of diabetes, and your blood sugar levels may not be high enough to show on every test. Some blood sugar test results can also vary day to day based on a variety of factors, like stress or illness.

Remember that your doctor will typically need to repeat any test to confirm your diagnosis.

There’s no existing cure for type 2 diabetes. But this condition is highly manageable with many effective treatment options.

If you’re over the age of 45, are experiencing symptoms of diabetes, or you have a condition that increases your diabetes risk, talk with your doctor about getting tested.

The first step is taking the tests and understanding your test results. It’s important to go over your results with your doctor. To confirm your diagnosis, your doctor will usually need to test you more than once.

If you’re diagnosed with diabetes, work with your doctor to start a treatment plan that’s right for you.

By following your treatment plan, you can help to avoid the complications of diabetes.