Diagnosing Diabetes and Learning About Prediabetes

There are several ways to diagnose diabetes. Each way usually needs to be repeated on a second day to diagnose diabetes.

Testing should be carried out in a health care setting (such as your doctor’s office or a lab). If your doctor determines that your blood glucose level is very high, or if you have classic symptoms of high blood glucose in addition to one positive test, your doctor may not require a second test to diagnose diabetes.

A1C FPG OGT

A1C

The A1C test measures your average blood glucose for the past 2 to 3 months. The advantages of being diagnosed this way are that you don't have to fast or drink anything.

  • Diabetes is diagnosed at an A1C of greater than or equal to 6.5%

Result

A1C
Normal less than 5.7%
Prediabetes 5.7% to 6.4%
 Diabetes 6.5% or higher

 

Fasting Plasma Glucose (FPG)

This test checks your fasting blood glucose levels. Fasting means after 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 at fasting blood glucose of greater than or equal to 126 mg/dl

Result

Fasting Plasma Glucose (FPG)
Normal less than 100 mg/dl
Prediabetes 100 mg/dl to 125 mg/dl
Diabetes 126 mg/dl or higher

 

Oral Glucose Tolerance Test (also called the OGTT)

The OGTT is a two-hour test that checks your blood glucose levels before and 2 hours after you drink a special sweet drink. It tells the doctor how your body processes glucose.

  • Diabetes is diagnosed at 2 hour blood glucose of greater than or equal to 200 mg/dl

Result

 Oral Glucose Tolerance Test (OGTT)
Normal  less than 140 mg/dl
Prediabetes  140 mg/dl to 199 mg/dl
Diabetes  200 mg/dl or higher

 

Random (also called Casual) Plasma Glucose Test

This test is a blood check at any time of the day when you have severe diabetes symptoms.

  • Diabetes is diagnosed at blood glucose of greater than or equal to 200 mg/dl

What is Prediabetes?

Before people develop type 2 diabetes, they almost always have "prediabetes" — blood glucose levels that are higher than normal but not yet high enough to be diagnosed as diabetes.

Doctors sometimes refer to prediabetes as impaired glucose tolerance (IGT) or impaired fasting glucose (IFG), depending on what test was used when it was detected. This condition puts you at a higher risk for developing type 2 diabetes and cardiovascular disease.

No Clear Symptoms

There are no clear symptoms of prediabetes, so, you may have it and not know it.

Some people with prediabetes may have some of the symptoms of diabetes or even problems from diabetes already. You usually find out that you have prediabetes when being tested for diabetes. 

If you have prediabetes, you should be checked for type 2 diabetes every one to two years.

Results indicating prediabetes are:

  • An A1C of 5.7% – 6.4%
  • Fasting blood glucose of 100 – 125 mg/dl
  • An OGTT 2 hour blood glucose of 140 mg/dl – 199 mg/dl

Preventing Type 2 Diabetes

You will not develop type 2 diabetes automatically if you have prediabetes. For some people with prediabetes, early treatment can actually return blood glucose levels to the normal range.

Research shows that you can lower your risk for type 2 diabetes by 58% by:

Don't worry if you can't get to your ideal body weight. Losing even 10 to 15 pounds can make a huge difference. 

Patient Education Materials — All About Prediabetes
This two-page introduction to prediabetes is in PDF format so you can download it, print it, and hand it out to patients.

You can also download the Spanish version.

 

  • Last Reviewed: December 9, 2014
  • Last Edited: December 9, 2014

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Diabetes Forecast