Diagnosis and Screening

Who should be tested?

The National Institute of Diabetes & Digestive & Kidney Diseases (NIDDK) recommends getting tested for diabetes if:

  • You have one or more risk factors and you are overweight.
  • You are experiencing symptoms.
  • You are 45 years of age or older, especially if you are overweight.

What are the tests for diabetes?

Your doctor can perform a number of tests to check if you suffer from diabetes. According to the American Diabetes Association, two abnormal results from any of the three tests on two different tests are necessary to diagnose diabetes.

  • Fasting plasma glucose (FPG) – Blood draw taken after eight hours without eating.
  • Casual plasma glucose (CPG) – Blood draw taken at any time, regardless of eating.
  • Oral glucose tolerance test (OGTT) - Blood draws taken at timed intervals over a three hour period after consuming a drink containing 75 grams of dissolved glucose in water.

Fasting Plasma Glucose (FPG) is the preferred test for Type 1 and Type 2 Diabetes. The American Diabetes Association lowered the diagnostic criteria to 126 mg/dL from the previous 140 mg/dL. Studies show that people with fasting plasma glucose of 126 mg/dL are at increased risk of complications affecting the eyes, nerves and kidneys. Casual plasma glucose may be used for testing when symptoms of diabetes are present.

Diabetes Test Diagnostic Ranges

  Diabetes Range Gestational Diabetes Range Pre-Diabetes Range
Fasting Plasma Glucose (FPG) 126 mg/dL or higher 95 mg/dL or higher 110-125 mg/dL*
Casual Plasma
Glucose (CPG)
200 mg/dL or higher + symptoms ----- -----
Oral Glucose
Tolerance Test (OGTT)
200 mg/dL or higher 180 mg/dL at 1 hour
155 mg/dL at 2 hours
140 mg/dL at 3 hours
41-199 mg/dL at 2 hr. interval**