Blood glucose levels are above normal in persons having diabetes. Most food components are turned into the sugar glucose to use for energy. The hormone insulin, which is made in an organ called pancreas, is needed to get glucose out of the bloodstream into the cells of our bodies. In diabetics there is not enough insulin produced or the body cells are not responding well to it. This causes sugar levels to build up in the blood after meals, which is affecting other body functions negatively.

In type 1 diabetes, also called insulin-dependent diabetes mellitus or juvenile-onset diabetes, the Langerhans' cells in the pancreas do not produce enough insulin. About 5% to 10% of all diagnosed cases of diabetes are of this type. In persons with type 2 diabetes the rate of glucose uptake of the body cells is not sufficient due to insuline resistance. About 90% to 95% of all diagnosed cases of diabetes are of this type. Gestational diabetes is a type of diabetes in 2% to 5% of all pregnant women with similarities to type 2 diabetes, but usually disappears when a pregnancy is over. Other specific types of diabetes resulting from specific genetic syndromes, surgery, drugs, malnutrition, infections, and other illnesses.

People with diabetes have a 2- to 4-fold increased risk of cardiovascular disease. Diabetes can also damage the kidneys, which not only can cause them to fail, but can also make them lose their ability to filter out waste products. People with diabetes do have a higher risk of blindness than people without diabetes. One of the most common complications of diabetes is diabetic neuropathy, leading to damage to the nerves that run throughout the body, connecting the spinal cord to muscles, skin, blood vessels, and other organs. As a result of the combination of these problems diabetics can develop many different foot problems when there is nerve damage in the feet or when blood flow is poor. As many as one-third of people with diabetes will have a skin disorder.

Patients with type 1 diabetes need insulin injections to keep blood glucose levels within safe levels. Many patients with type 2 diabetes can supplement insulin levels with oral medication to control their blood glucose levels. Healthy eating, physical activity, and blood glucose testing are essential for both conditions. The use of insulin to prevent blood glucose levels from going too low or too high must be learned with the help of a health care provider.

In persons with pre-diabetes blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes. The condition is also referred to as Impaired Glucose Tolerance or Impaired Fasting Glucose (IGT/IFG), depending on which test was used to detect it. Such people are likely to develop diabetes and are at higher risk of cardiovascular disease. people with pre-diabetes can delay or prevent the onset of type 2 diabetes through lifestyle changes.

Either the fasting plasma glucose test (FPG) or the oral glucose tolerance test (OGTT) are used to detect pre-diabetes. With the FPG test the level of blood glucose is measured after a longer period of fasting (early the morning, before breakfast), while in the OGTT, a person's blood glucose is checked after fasting and again 2 hours after drinking a glucose-rich drink. Normal fasting blood glucose is below 100 mg/dl. A person with pre-diabetes has a fasting blood glucose level between 100 and 125 mg/dl. If the blood glucose level rises to 126 mg/dl or above, a person has diabetes. In the OGTT test normal blood glucose is below 140 mg/dl 2 hours after the drink. In pre-diabetes, the 2-hour blood glucose is 140 to 199 mg/dl. If the 2-hour blood glucose rises to 200 mg/dl or above, a person has diabetes.