Hyperglycemic Hyperosmolar Nonketotic Coma (HHNKC)

An Extremely Serious Complication of Type 2 Diabetes

Nurse giving blood sugar test to patient in home
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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. HHNKC can happen to people with either type 1 or type 2 diabetes that is not being controlled properly, but it occurs more often in people with type 2.

HHNKC is also known as diabetic hyperglycemic hyperosmolar coma (HHOC), hyperosmolar nonketotic coma (HONK), hyperosmolar hyperglycemic state (HHS) or hyperosmolar hyperglycemic nonketotic syndrome (HHNS).

In HHNKC, blood sugar levels rise, and your body tries to get rid of the excess sugar by passing it into your urine. You make lots of urine at first, and you have to go to the bathroom more often. Later you may not have to go to the bathroom as often, and your urine becomes very dark. Also, you may be very thirsty. Even if you are not thirsty, you need to drink liquids. If you don't drink enough liquids at this point, you can get dehydrated.

If HHNKC continues, the severe dehydration will lead to seizures, coma and eventually death. HHNKC may take days or even weeks to develop.


HHNKC is caused by severely elevated blood glucose levels, usually over 600 mg/dl.


  • Blood sugar level over 600 mg/dl
  • Dry, parched mouth
  • Extreme thirst (although this may gradually disappear)
  • 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

HHNKC frequently happens in the elderly and is usually precipitated by another illness, such as infection or flu, or sometimes a chronic condition such as congestive heart failure or renal failure. HHNKC is an emergency that requires immediate medical care.

HHNKC can lead to:

  • Seizures
  • Heart attack
  • Stroke
  • Coma

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

How to Avoid HHNKC

HHNKC only occurs when diabetes is uncontrolled. The best way to avoid HHNKC is to check your blood sugar regularly. Many people check their blood sugar several times a day, such as before or after meals. Talk with your health care team about when to check and what the numbers mean. You should also talk with your healthcare team about your target blood sugar range and when to call if your blood sugars are too high, or too low and not in your target range. When you are sick, you will check your blood sugar more often, and drink a glass of liquid (alcohol-free and caffeine-free) every hour. Work with your team to develop your own sick day plan.

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