An Overview of Hyperglycemic Hyperosmolar Nonketotic Coma (HHNKC)

An Extremely Serious Complication of Type 2 Diabetes

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Hyperglycemic hyperosmolar nonketotic coma (HHNKC) is an extremely serious complication of type 2 diabetes, most often occurring in those who are non-insulin dependent. It is also known as diabetic coma. HHNKC is a life-threatening condition that can happen to people with either type 1 or type 2 diabetes when the disease is not being controlled properly, but it occurs more often in people with type 2, especially the elderly.

HHNKC is also known as diabetic hyperglycemic hyperosmolar coma (HHOC), hyperosmolar nonketotic coma (HONK), hyperosmolar hyperglycemic state (HHS) or hyperosmolar hyperglycemic nonketotic syndrome (HHNS). HHNKC differs from diabetic ketoacidosis, which involves high levels of ketoacids in the blood.


If you are experiencing HHNKC, you may be unconscious and unable to interact with your environment. There are several warning signs that you might be at risk of HHNKC, including:

  • Blood glucose (sugar) level over 600 mg/dl
  • Blood becomes thicker than usual
  • Dry, parched mouth
  • Extreme thirst (although this may gradually disappear)
  • Frequent urination
  • Warm, dry skin that does not sweat
  • High fever (over 101 degrees Fahrenheit, for example)
  • Sleepiness or confusion
  • Loss of vision
  • Hallucinations (seeing or hearing things that are not there)
  • Weakness on one side of the body

Note: If you have any of the above symptoms, call someone on your healthcare team immediately.


HHNKC usually occurs in people with type 2 diabetes who have severely elevated blood glucose levels: over 600 mg/dl. When glucose rises that high, the body tries to get rid of the excess sugar by passing it into your urine. At first, you may need to urinate frequently. Later, you may not have to go to the bathroom as often, and your urine becomes very dark. You may also be extremely thirsty as your body tries to replenish lost liquids. Even if you are not thirsty, it is important that you drink liquids to prevent dehydration.

Excessive urination and extreme thirst mean you may be at risk of severe dehydration, which could lead to seizures, heart attack, coma, or death. HHNKC may take days or even weeks to develop.

HHNKC most frequently happens in the elderly may be caused by the following factors:

  • Having another illness, such as infection or flu
  • Having another chronic condition such as congestive heart failure or renal failure
  • Having diabetes that is uncontrolled or managed appropriately, such as by not taking diabetes medications as prescribed
  • Taking other medications that increase urination, such as diuretics, or that may affect blood sugar, such as glucocorticoids


HHNKC is an emergency that requires immediate medical care. The condition may be diagnosed via blood glucose test or via testing the body's water balance and electrolyte levels, like in a serum osmolality test.


If you're experiencing a diabetic coma, you need urgent treatment, as you could be at risk for brain damage or death. Medical care usually involves saline solution, insulin, and electrolyte replenishment to bring down glucose levels and rehydrate the body.


The best way to avoid the risk of HHNKC is to keep your blood sugar under control through medication, regular glucose tests, and healthy lifestyle habits.

  • Test your blood sugar multiple times per day, especially before and after meals, and more frequently if you are sick.
  • Be sure to take any prescribed medicines as directed by your physician and/or pharmacist.
  • Keep up with hydration, aiming for an average of 64 ounces of water daily.
  • Reach out to your healthcare team if your blood sugar rises above 300 mg/dl twice in one day.

A Word From Verywell

The prospect of HHNKC or diabetic coma can be scary and worrisome if you have diabetes. Work with your doctor and care providers to make sure that your condition is well-managed, and to establish protocols in case of emergency.

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  • American Diabetes Association.  "Hyperosmolar Hyperglycemic Nonketotic Syndrome (HHNS).”