Diagnosing Diabetes

Diagnosing diabetes can be done with an oral glucose tolerance test or a fasting plasma glucose test. The fasting plasma glucose test is the preferred test for diagnosing diabetes because of its convenience, although the oral glucose tolerance test is more accurate. Diagnosing diabetes in pregnant women is based on plasma glucose values measured during the oral glucose tolerance test.

 

Diagnosing Diabetes: An Overview

In people with
 diabetes, the pancreas either produces little or no insulin, or the cells do not respond appropriately to the insulin that is produced. Glucose builds up in the blood, overflows into the urine, and passes out of the body. Thus, the body loses its main source of fuel even though the blood contains large amounts of glucose.
 
In pre-diabetes, blood glucose levels are higher than normal but not high enough to be characterized as diabetes.
 
The fasting plasma glucose test is the preferred test for diagnosing diabetes -- both type 1 or type 2 diabetes. It is most reliable when done in the morning; however, a diagnosis of diabetes can be made after positive results with any one of three tests, with confirmation from a second positive test on a different day:
 
  • A plasma glucose value of 126 mg/dL or more after a person has fasted for eight hours.
     
  • An oral glucose tolerance test (OGTT) plasma glucose value of 200 mg/dL or more in a blood sample taken two hours after a person has consumed a drink containing 75 grams of glucose dissolved in water. This test, taken in a laboratory or the doctor's office, measures plasma glucose at timed intervals over a three-hour period.
     
  • A random (taken any time of day) plasma glucose value of 200 mg/dL or more, along with the presence of diabetes symptoms.
     
(Diagnosing Diabetes Continued: Page 2)
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Written by/reviewed by: Arthur Schoenstadt, MD
Last reviewed by: Arthur Schoenstadt, MD
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