A1c testsThe A1C test is a common blood test used to diagnose type 1 and type 2 diabetes and then to gauge how well you're managing your diabetes. The A1C test . When the A1C test is used to diagnose diabetes, an A1C level of 6.5 percent or higher on two separate tests indicates you have diabetes. A result between 5.7 . Defines and explains the A1C diabetes blood test. Discusses using the test for diagnosis of diabetes and prediabetes and monitoring of glucose levels in people .