How is diabetes diagnosed?

Diabetes is diagnosed with fasting sugar blood tests or with A1c blood tests, also known as glycated hemoglobin tests. A fasting blood sugar test is performed after you have had nothing to eat or drink for at least eight hours. Normal fasting blood sugar is less than 100 mg/dl (5.6 mmol/l). You do not have to be fasting for an A1c blood test. Diabetes is diagnosed by one of the following (see chart):

  • Your blood sugar level is equal to or greater than 126 mg/dl (7 mmol/l).
  • You have two random blood sugar tests over 200 mg/dl (11.1 mmol/l) with symptoms.
  • You have an oral glucose tolerance test with results over 200 mg/dl (11.1 mmol/l).
  • Your A1c test is greater than 6.5 percent on two separate days.

An A1c test should be performed in a laboratory using a method that is certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized to the Diabetes Control and Complications Trial (DCCT) assay.

Type of testNormalPre-diabetesDiabetes
Fasting
glucose test

Less than 100

100-125126 or higher
Random (anytime)
glucose test

Less than 140

140-199200 or higher
A1c test

Less than 5.7%

5.7 - 6.4%6.5% or higher

Last reviewed by a Cleveland Clinic medical professional on 10/02/2018.

References

  • American Diabetes Association. Diabetes Basics. Accessed 6/8/2020.
  • The National Institute of Diabetes and Digestive and Kidney Diseases. What is Diabetes? Accessed 6/08/20.
  • American Diabetes Association. A1C and eAG. Accessed 6/8/2020.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy