Diabetes is a condition of elevated blood sugar where the body does not produce enough insulin or the body is unable to respond properly to the insulin that is produced. Insulin is a hormone that is made in the pancreas, which is a small organ situated behind the stomach. Insulin is important because it moves glucose, a simple sugar, from the blood into the body's cells. It also has a number of other important effects on metabolism.

The foods people eat provide the body with glucose, which is used by the cells as a source of energy. If insulin isn't available or doesn't work correctly to move glucose from the blood into the cells, glucose will stay in the blood. High blood glucose levels are toxic. Cells that don't get glucose are lacking the fuel they need to work properly. The symptoms of diabetes are a result of high sugar levels in the blood.

Diabetes is diagnosed by taking a blood glucose level. When screening for diabetes, the physician or primary health care provider might take what is called a "random" blood sugar level. This is a sugar level that is taken at any time of the day, without any specific preparation and independent of the food that has been eaten. A random blood sugar level of at least 11.1 mmol/L can be used to diagnose diabetes.

Other diagnostic tests can include the measurement of a fasting blood sugar level. A fasting blood sugar of at least 7.0 mmol/L can be used to diagnose diabetes.

Also, a 75 g oral glucose tolerance test (OGTT) can be used to diagnose diabetes. A 2-hour blood sugar level of at least 11.1 mmol/L after an OGTT can be used to diagnose diabetes.

Lastly, an A1C (which measures the average blood sugar levels over the past 2 to 3 months) of at least 6.5% can be used to diagnose diabetes. A1C is not used to diagnose diabetes for children, adolescents, pregnant women, or people with suspected type 1 diabetes.

It is important to note that one high blood glucose reading or A1C does not necessarily mean you have diabetes. If you are not having any symptoms of diabetes (such as unusual thirst, frequent urination, weight changes, fatigue, frequent infections, or blurred vision), at least 2 high blood glucose or A1C readings are required before your doctor will make a diagnosis.