Aging & Health A to Z
Diagnosis & Tests
Finding out if you have diabetes early is essential to your health. The sooner you begin treating it, the easier it will be to avoid serious problems later on.
Diagnosis is simple. Your healthcare provider can use one or more of the following tests to diagnose diabetes.
Fasting Blood Glucose Testing
In this test, your blood is drawn after you have had nothing to eat or drink (except water) for 8 hours. Blood glucose is measured in units called milligrams per deciliter (mg/dL). A normal fasting blood glucose level is 100 mg/dL or less. The test is usually repeated a second time. Diabetes is diagnosed when two fasting blood glucose levels measure 126 mg/dL or higher.
Oral Glucose Tolerance Test
In this test, a blood sample is taken before you drink a sugary beverage, and again 2 or 3 hours after. This test is usually used if your fasting blood glucose test was normal, but your symptoms make your healthcare provider suspect that you have pre-diabetes or type 2 diabetes.
Casual or Random (non-fasting) Blood Glucose Test
If you have diabetes symptoms or risk factors, your healthcare provider might perform this simple in-office blood test by taking a drop of blood from your finger. You don’t need to fast before the test. A glucose level of 200 mg/dL or higher usually indicates diabetes.
Hemoglobin A1c (HbA1c) Test
The HbA1c test is used to establish a diagnosis of diabetes, and then is used every 3 months to monitor the disease. (It is frequently referred to as an A1c test.) An A1c reading of 6.5% or more indicates diabetes. The American Diabetes Association recommends that most adults should have a reading of 7% or less, including healthy older adults. However, for older adults with multiple medical problems, an A1c reading of less than 8% or 8.5% may be acceptable. You should discuss your goal level with your healthcare provider.
Medications can sometimes raise your blood sugar, so give your healthcare provider a complete list of everything you’re taking before your blood test. Make sure to include all prescriptions, over-the-counter medications, vitamins, herbal and other supplements in the list.
Updated: January 2018
Posted: March 2012