Glycated hemoglobin is a form of hemoglobin where the hemoglobin is bound to glucose. This level depends on the amount of glucose in the blood plasma when the red blood cell is formed. As such, there is a normal level of glycated hemoglobin in patients with normal blood glucose levels. Where a glucose metabolism disease, like diabetes mellitus, is suspected, the glycated hemoglobin level is tested to show blood glucose levels over a roughly three month period - the average life span of a red blood cell. For example, a patient with diabetes may test consistently normal with respect to blood glucose, but if their glycated hemoglobin levels are high, it probably indicates that their blood sugar levels are still not under control.