Diabetic Coma

Coma is relatively rare in diagnosed diabetes
Coma is relatively rare in diagnosed diabetes

Coma is relatively rare in diagnosed diabetes but it is very important to be aware of the situations that increase risk of coma.

Causes of diabetic coma

The main causes of coma occurring in people with diabetes are as a result of very low or very high blood glucose levels.

The three most common causes of coma in people with diabetes are:

Severe hypoglycemia and coma

Severe hypoglycemia (very low blood glucose levels) can lead to loss of consciousness and coma if not treated.

In most cases the body will restore blood sugar levels to normal by releasing glucagon to raise blood sugar levels.

Coma is more likely to occur from low blood glucose levels if:

  • A large insulin overdose is taken
  • Alcohol is in the body during hypoglycemia
  • Exercise has depleted the body’s glycogen supply

Diabetic ketoacidosis and coma

Diabetic ketoacidosis is a dangerous state of having very high blood glucose levels (typically above 17 mmol/L) in combination with high ketone levels.

Ketoacidosis is able to occur if the body runs out of insulin and is therefore a factor for people with type 1 diabetes to be aware of. Insulin can prevent ketone levels rising and this is the key reason why people with diabetes are advised never to miss their long term (basal) insulin injections.


Coma is one of the most dangerous complications which can result from diabetes. Coma is a serious state of unconsciousness in which someone is unresponsive and cannot be woken up.

In people with diabetes, the most common causes of coma are very high or very low blood glucose. Very low blood glucose levels which lead to coma can happen if people inject too much insulin for the meals and activities they are undertaking.

In type 1 diabetes, a dangerous short term complication known as ketoacidosis can occur which can lead to coma if it is not treated quickly. Charity Diabetes UK advises people with type 1 diabetes to test for ketones if their blood glucose levels rise above 15 mmol/l.

People with type 2 diabetes are less likely to experience ketoacidosis but can develop a dangerous condition known as Hyperosmolar Hyperglycemic State which can lead to coma.

Hyperosmolar Hyperglycemic State may occur if blood glucose levels are very high, typically over 40 mmol/l.

It is important to be able to recognise the symptoms of very low and very high blood glucose levels to prevent these conditions leading to coma.

The symptoms of very low blood glucose include:

  • Difficulty concentrating
  • Confusion or panic
  • Disorderly or irrational behaviour
  • Convulsions

The symptoms of very high blood glucose include:

  • Nausea
  • Vomiting
  • Dehydration
  • Unusual breathing, either rapid or laboured breathing
  • Extreme thirst
  • Disorientation
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The symptoms of ketoacidosis include nausea, vomiting, dehydration, disorientation and deep, laboured breathing.

If someone with diabetes is displaying these symptoms call for emergency medical help as loss of consciousness and coma could follow.

Illness in type 1 diabetes can lead to high blood glucose and ketone levels. It is advisable to test for ketones during periods of illness to prevent ketoacidosis developing.

Diabetic coma at diagnosis of type 1 diabetes

If the symptoms of type 1 diabetes are not spotted soon enough, ketoacidosis can develop leading to coma before a diagnosis is made.

It is possible that doctors may not correctly diagnose diabetes at first presentation. Approximately 1 in 4 patients diagnosed with type 1 diabetes are recorded as demonstrating signs of ketoacidosis.

Nonketotic hyperosmolar coma

In type 2 diabetes, insulin levels in the body are usually present to stop ketone levels rising too high. However, at very blood glucose levels (typically above 33 mmol/L) a dangerous condition called Hyperosmolar Hyperglycaemic State (HHS) can develop.

Periods of illness or lack of sufficient diabetes medication could lead to development of Hyperosmolar Hyperglycaemic State.

Symptoms of HHS include extreme thirst, disorientation, nausea and vomiting.

If someone with diabetes has the above symptoms call for medical help as losing consciousness and coma (hyperglycaemic hyperosmolar non-ketotic coma) can follow.

Preventing diabetic coma

The following recommendation can help to prevent diabetic coma from occurring: