Blood glucose test results recorded in a chart format by a diabetic. The dots represent the blood sugar (glucose) levels from previous tests. For a person with diabetes, high blood sugar may be caused by missed medication (insulin) doses, eating too many calories, lack of exercise, illness or stress. The glucometer (left) is used to test the glucose levels of a diabetes sufferer. A blood sample is analysed by the machine and the result is displayed on the digital screen. Diabetes is a metabolic disorder in which unused sugars (such as glucose) accumulate in the blood and urine. Monitoring of blood glucose levels allows diabetics to control the disease through diet or medication such as insulin injections.