There are two laboratory blood tests used to arrive at a diabetes diagnosis:
The first is called a fasting plasma glucose test. This test requires a blood sample after an overnight fast (no eating or drinking for eight hours). If the person you're caring for has symptoms that indicate diabetes and her fasting blood sugar reading is above 126 milligrams per deciliter of blood (mg/dL), diabetes is diagnosed.
The second test is known as the oral glucose tolerance test. After an overnight fast, a patient will be given a blood test and, immediately afterward, a sugary beverage to drink. Another blood sample is taken two hours later. If the initial blood sugar reading is above 126 mg/dL and/or her two-hour test result is above 200 mg/dL, the doctor can make a diabetes diagnosis.