Diabetic coma is a rare but serious occurrence. It is important to be aware of the risks of coma in diabetic patients and the possible causes.

Diabetes mellitus is typically characterized by high blood sugar and an inability to reduce this sugar level. This may be due to a true (as in type 1) or relative (as in type 2) deficiency of insulin, the hormone responsible for lowering blood sugar.

The three most common causes of coma in diabetic patients are:

• Very low blood sugar or severe hypoglycaemia

  If the blood sugar level in the brain drops to a critical level (below 3.5 mmol/l), a person is at risk of losing consciousness and falling into a diabetic coma. Normally, as blood sugar begins to fall, the body compensates for this by releasing glucagon, a hormone that opposes the actions of insulin by raising blood glucose. A coma is more likely to occur if an individual has taken an overdose of insulin or other anti-diabetic medications, consumed a lot of alcohol or taken part in an unusual amount of exercise (especially if they are also on insulin).

• Diabetic ketoacidosis

  This is mostly seen in people with type 1 diabetes or those who are taking insulin. If there is shortage of insulin, the body fails to use the glucose in the blood for energy and instead fats are broken down to provide it, which forms acidic compounds called ketones. A build up ketones in the body causes a condition called ketoacidosis. Ketoacidosis may occur as a result of a missed dose of insulin or as a result of acute infection, injury or surgery causing a rise in hormones that counteract the effects of insulin.

• Hyperosmolar hyperglycemic state (HHS)

  This condition is characterized by severe dehydration and very high blood glucose. A missed dose of insulin, acute infection or injury, and heavy food or sugar intake are the most commonly causes of HHS severe enough to lead to coma. This type of coma develops slowly over several days or weeks.