Tests Used to Diagnose Diabetes
Hemoglobin A1c (HbA1c) Test
The HbA1c, or A1c, is a blood test that shows your average blood sugar level over the past 3 months. An A1c level of 6.5% or higher is used to diagnose diabetes.
Fasting Blood Glucose Testing
Blood is drawn after fasting (nothing to eat or drink except water for at least 8 hours). A normal fasting blood glucose level is 100 mg/dL or lower. Two fasting blood glucose results of 126 mg/dL or higher indicate diabetes.
Oral Glucose Tolerance Test
A blood sample is taken before drinking a sugary drink and again 2 hours later. This test is used less often in older adults. A blood glucose level over 200 mg/dL suggests diabetes.
Non-fasting Blood Glucose Test
A non-fasting blood glucose test may be done as part of routine blood work. A glucose level of 200 mg/dL or higher may suggest diabetes.
Last Reviewed and Updated: August 2026
By: AGS/HiAF Public Education Committee, HealthinAging.org Content Reviewers