How is diabetes diagnosed?

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How is diabetes diagnosed?

Diabetes is diagnosed and managed by checking your glucose level in a blood test. There are three tests that can measure your blood glucose level: fasting glucose test, random glucose test and A1c test.

  • Fasting plasma glucose test: This test is best done in the morning after an eight hour fast (nothing to eat or drink except sips of water).
  • Random plasma glucose test: This test can be done any time without the need to fast.
  • A1c test: This test, also called HbA1C or glycated hemoglobin test, provides your average blood glucose level over the past two to three months. This test measures the amount of glucose attached to hemoglobin, the protein in your red blood cells that carries oxygen. You don’t need to fast before this test.
  • Oral glucose tolerance test: In this test, blood glucose level is first measured after an overnight fast. Then you drink a sugary drink. Your blood glucose level is then checked at hours one, two and three.

Type of testNormal
(mg/dL)Prediabetes
(mg/dL)Diabetes
(mg/dL)Fasting
glucose test

Less than 100

​

100-125126 or higherRandom (anytime)
glucose test

Less than 140

​

140-199200 or higherA1c test

Less than 5.7%

​

5.7 - 6.4%6.5% or higherOral glucose
tolerance testLess than 140140-199200 or higher

Gestational diabetes tests: There are two blood glucose tests if you are pregnant. With a glucose challenge test, you drink a sugary liquid and your glucose level is checked one hour later.

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