According to the American Diabetes Association, the only way for a person to know if he has diabetes is to be tested; however, several common symptoms can indicate that a visit to the doctor is needed. These symptoms include frequent urination; feeling thirsty or hungry, especially after having already eaten; fatigue; blurred vision or cuts and bruises that are slow to heal.
There are additional symptoms based on the type of diabetes, according to the American Diabetes Association. These include losing weight even if the person is eating more for type 1 diabetes and numbness or tingling in the hands or feet for type 2.
The ADA notes that there are several tests that a doctor may use to determine if a patient has diabetes. These tests often require multiple visits to the doctor's office; however, if the doctor determines that the patient's blood glucose is very high or he has the above symptoms after one positive test, the doctor may not require additional testing. Many of the tests, such as the Oral Glucose Tolerance Test and the Fasting Plasma Glucose test, require the patient to fast for several hours. The A1C measures a person's average glucose level over a period of several months. The doctor determines which test, if any, needs to be performed.