What is Hyperglycemic Hyperosmolar Nonketotic Syndrome?

Protecting Yourself From the Dangers of a Diabetic Coma

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Hyperglycemic hyperosmolar nonketotic syndrome (HHNS) is a potentially deadly condition that can develop as a result of infection or illness in people with uncontrolled type 2 diabetes or when diabetes medications aren't taken as directed. Some also refer to this as a "diabetic coma."

HHNS is a relatively rare complication of diabetes, accounting for just 1% of hospital admissions among people with diabetes.

HHNS is sometimes referred to by other names:

  • Hyperglycemic hyperosmolar nonketotic coma (HHNK)
  • Nonketotic hyperosmolar syndrome (NKHS)
  • Diabetic hyperosmolar syndrome
  • Diabetic HHS
  • Hyperosmolar coma
  • Hyperosmolar hyperglycemic state


The symptoms of HHNS may appear slowly, taking days or even weeks to fully develop. Common symptoms include:

  • Blood glucose levels over 600 milligrams per deciliter (mg/dl)
  • Frequent urination
  • Extreme thirst
  • Dry mouth
  • Confusion or sleepiness
  • Unexpected weight loss
  • Skin that is warm and dry without sweating
  • Fever (usually over 101 F)
  • Weakness or paralysis on one side of the body
  • Loss of vision
  • Hallucinations

If you have symptoms of extreme thirst, frequent urination, confusion, and blurry vision, it's important that you seek medical care immediately, as you could be experiencing symptoms of hyperglycemia, which may be life-threatening.

Ellen Lindner / Verywell


HHNS develops when glucose levels surge (typically above 600 mg/dl), leading to severe dehydration. This dehydration occurs because elevated levels of glucose cause blood to become thicker and result in the body needing to produce more urine in order to lower them.

The result is frequent urination, which can result in serious or even life-threatening dehydration. If these fluids are not adequately replenished, the condition may eventually result in a seizure, coma, or even death.

HHNS is typically brought on by:

  • An infection, such as pneumonia or a urinary tract infection
  • Poor management of blood sugar and/or not taking diabetes medications as prescribed
  • Taking certain medications, such as glucocorticoids (which alter glucose levels) and diuretics (which increase urine output)
  • Trauma and other medical emergencies like cardiovascular disease
  • Having chronic conditions in addition to diabetes, such as congestive heart failure or kidney disease

Most people who experience HHNS are 65 and have type 2 diabetes. Young people with type 1 diabetes and children can be affected by HHNS as well, especially if they're obese, although this is uncommon.

The condition is more likely to affect older adults, and especially those of African-American, Native American, or Hispanic ethnic backgrounds. Rarely, HHNS can occur in people who have not yet been diagnosed with diabetes.


HHNS is diagnosed based on symptoms and by measuring blood glucose levels, which can be performed with a finger stick.

A blood glucose level of 600 mg/dL and low ketone levels are the main factors for diagnosis of HHNS.

Serum osmolality, a test that measures the body's water/electrolyte balance, also is used to diagnose HHNS. Serum osmolality specifically measures the chemicals dissolved in the liquid part of blood (serum), such as sodium, chloride, bicarbonate, proteins, and glucose. The test is done by taking a sample of blood from a vein.


Treatment typically involves starting intravenous (IV) fluids (saline solution delivered through a needle into a vein) to rehydrate the body quickly. It also may require IV insulin to bring down blood sugar levels.

Potassium and sometimes sodium phosphate replenishment may also be required to support cell function.

If you are hospitalized due to HHNS, you may be kept overnight for observation. The main goal of treatment of this condition is to identify the underlying factors, whether that's an infection, a certain medication, or poor blood sugar management.

It is imperative that a person experiencing HHNS receive urgent professional medical care, as complications may include seizures, coma, swelling of the brain, or even death if left untreated.


The best way to prevent this serious condition is to manage your diabetes by:

  • Checking your blood sugar according to your healthcare provider’s instructions. When you are sick, you should check your blood every four hours. Your blood sugar tends to be naturally higher when your body is fighting a virus or infection.
  • Taking your diabetes medications, including insulin, as directed by your healthcare provider
  • Drinking an ample amount of fluid each day, especially when you are ill
  • Staying in contact with your diabetes healthcare team when your blood sugar is consistently above 300 mg/dl
  • Staying up-to-date on vaccinations, including getting an annual flu shot and discussing with your healthcare provider the advisability of getting the pneumococcal vaccine

How Is HHNS Different From Diabetic Ketoacidosis (DKA)?

DKA is also a serious condition and potentially life-threatening if not treated promptly. In contrast to HHNS, DKA is almost exclusively a condition that occurs in people with type 1 diabetes.

A lack of insulin causes a build-up of glucose in the blood that cannot get into the cells of the body to be used for energy. The body compensates by looking for an alternative energy source in stored fat. When stored fat is used for energy it creates a toxic waste product called ketones, which can poison the body.

HHNS does not produce ketones, and the symptoms of DKA are different, including:

  • Breath that has a fruity odor
  • Labored breathing
  • Nausea and vomiting
  • A rapid and weak pulse
  • Abdominal pain

A Word From Verywell

The best way to prevent HHNS is by keeping your blood sugar levels under control. Test them regularly using a glucometer, work with your healthcare provider to make sure you're taking any diabetes medications as prescribed, and learn the warning signs of elevated glucose levels and dehydration, such as extreme thirst and frequent urination, so you know to seek treatment when you need it. Educate your loved ones and coworkers to also recognize the early si gns of blood sugar imbalance, so they can send for help, too.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Gary Gilles
Gary Gilles is a licensed clinical professional counselor (LCPC) who has written about type 1 diabetes and served as a diabetes counselor. He began writing about diabetes after his son's diagnosis as an infant.