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Diagnosing Diabetes

Protocol for diagnosing diabetes

According to the National Institute of Diabetes and Digestive and Kidney Diseases:

  • People over age 45 should be tested for prediabetes or diabetes. If the first blood glucose test is normal, they should be retested every 3 years.

  • People under age 45 should consider getting tested for prediabetes or diabetes if they have a body mass index (BMI) of greater than or equal to 25 kg/m2 and have 1 or more of the following risk factors:

    • Having a first-degree relative with diabetes (mother, father, or sibling)

    • Being a member of a high-risk ethnic group (African-American, Hispanic, Asian, Pacific Islander, or Native American)

    • Delivering a baby weighing more than 9 pounds, or having diabetes during pregnancy

    • Having blood pressure at or above 140/90 mm/Hg

    • Having abnormal blood fat levels, such as high-density lipoproteins (HDL) less than or equal to 35 mg/dL, or triglycerides greater than or equal to 250 mg/dL (mg/dL = milligrams of glucose per deciliter of blood)

    • Having a sedentary lifestyle

    • Having impaired glucose tolerance when previously tested for diabetes

    • Having polycystic ovarian syndrome

A diagnosis of diabetes

A1C greater than or equal to 6.5%

  • Fasting plasma glucose of greater than or equal to 126 mg/dL

  • Casual plasma glucose (taken at any time of the day) of greater than or equal to 200 mg/dL with the symptoms of hyperglycemia or hyperglycemic crisis

  • Oral glucose tolerance test (OGTT) value of greater than or equal to 200 mg/dL. The OGTT is obtained 2 hours after a drink containing glucose has been consumed, which occurs after fasting for at least 8 hours.

A diagnosis of gestational diabetes

Gestational diabetes may be diagnosed with 1 of 2 approaches:

One-step approach

A 75-gram glucose tolerance test, which involves drinking a glucose drink. Blood glucose measurements are taken when patient is fasting (at least 8 hrs), 1 hour after drink, and 2 hours after drink. This test is done at 24 to 28 weeks gestation in women not previously diagnosed with diabetes. A diagnosis of gestational diabetes is made when any one of the following blood glucose levels are met or exceeded: 

  • Fasting: 92 mg/dL

  • 1 hour: 180 mg/dL

  • 2 hour: 153 mg/dL

Two-step approach

This test is also done at 24 to 28 weeks gestation in women not previously diagnosed with diabetes.

  • Step 1: A 50-gram glucose tolerance test with a blood glucose measurement at 1 hour. If the blood glucose at 1 hour is greater than or equal to 140 mg/dL, then proceed to step 2.  

  • Step 2: A100-gram glucose tolerance test is done while patient is fasting. A diagnosis of gestational diabetes is made when at least 2 of the following blood glucose levels are met or exceeded:  

    • Fasting: 105 mg/dL

    • 1 hour: 190 mg/dL

    • 2 hour: 165 mg/dL

    • 3 hour: 145 mg/dL

Consult your doctor regarding your wish to be screened for gestational diabetes.

Online Medical Reviewer: Grantham, Paula, RN, BSN
Online Medical Reviewer: MMI board-certified, academically affiliated clinician
Online Medical Reviewer: Turley, Ray, BSN, MSN
Date Last Reviewed: 2/5/2014
© 2000-2016 The StayWell Company, LLC. 780 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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