Hyperosmolar Hyperglycemic Syndrome


What is hyperosmolar hyperglycemic syndrome (HHS)?

Hyperosmolar hyperglycemic syndrome (HHS) is a serious complication of diabetes mellitus. HHS occurs when a person’s blood glucose (sugar) levels are too high for a long period, leading to severe dehydration (extreme thirst) and confusion.

Hyperosmolar hyperglycemic syndrome is also known by many other names, including:

  • Diabetes-related HHS.
  • Diabetes-related hyperosmolar syndrome.
  • Hyperglycemic hyperosmolar nonketotic coma (HHNK).
  • Hyperosmolar coma.
  • Hyperosmolar hyperglycemic nonketotic syndrome (HHNS).
  • Hyperosmolar hyperglycemic state.
  • Nonketotic hyperosmolar syndrome (NKHS).

Who is affected by hyperosmolar hyperglycemic syndrome (HHS)?

HHS most often affects people who have type 2 diabetes who are:

  • Older (usually in their 60s or 70s).
  • African-American, Native American or Hispanic.
  • Affected by other health issues, such as infection, illness or heart conditions.

HHS can be fatal if it’s not treated. Rarely, HHS can affect children and young adults who have type 1 or type 2 diabetes, especially if they have obesity. Very rarely, people who have not yet been diagnosed with diabetes can develop HHS.

How common is hyperosmolar hyperglycemic syndrome (HHS)?

HHS is less common than other major complications associated with diabetes. HHS accounts for less than 1% of hospital admissions for people with diabetes.

Symptoms and Causes

What causes hyperosmolar hyperglycemic syndrome (HHS)?

People who have diabetes have too much glucose (sugar) in their blood. The glucose builds up because their bodies either don’t make enough insulin, or have trouble using the insulin that they do make. (Insulin is a naturally occurring hormone, produced by the beta cells of the pancreas, which helps the body use sugar for energy.)

HHS occurs when the blood sugar of a person with diabetes becomes too high (hyperglycemia) for a long time. The extra sugar is passed into the urine, which causes the person to urinate frequently. As a result, he or she loses a lot of fluid, which can lead to severe dehydration (extreme thirst).

HHS usually develops in people who do not have their type 2 diabetes under control and they:

  • Have an illness or infection, such as pneumonia or a urinary tract infection.
  • Stop taking medication to manage their diabetes.
  • Have a heart attack or stroke.
  • Take certain medications—such as steroids or diuretics—that can cause the syndrome.

What are the symptoms of hyperosmolar hyperglycemic syndrome (HHS)?

Symptoms of HHS usually come on slowly, and can take days or weeks to develop. Symptoms include:

  • High blood sugar level (over 600 mg/dL).
  • Confusion, hallucinations, drowsiness or passing out.
  • Dry mouth and extreme thirst that may eventually get better.
  • Frequent urination.
  • Fever over 100.4 degrees Fahrenheit.
  • Blurred vision or loss of vision.
  • Weakness or paralysis that may be worse on one side of the body.

Diagnosis and Tests

How is hyperosmolar hyperglycemic syndrome (HHS) diagnosed?

You should seek medical attention right away if you have diabetes and you have these symptoms:

  • Extreme thirst.
  • Frequent urination.
  • Confusion, or a change in your mental state.
  • Changes in your vision.

Your doctor will examine you, ask about your symptoms, and order a blood test to check your blood sugar level. A very high blood sugar level (over 600 mg/dL) with low ketone levels (acids in blood and urine) will help the doctor make a diagnosis of HHS.

Management and Treatment

How is hyperosmolar hyperglycemic syndrome (HHS) treated?

To treat HHS, your doctor will give you intravenous (IV) medications. These include:

  • Fluids to hydrate you.
  • Electrolytes (such as potassium) to balance the minerals in your body.
  • Insulin to control your blood sugar levels.

Your doctor will also treat any underlying conditions or infections that may have caused the HHS. You will usually stay in the hospital so that your healthcare team can watch you closely for any complications.

What are the side effects of the treatment for hyperosmolar hyperglycemic syndrome (HHS)?

The IV electrolytes or fluids used to treat dehydration do not have side effects. Side effects from insulin include:

Your doctor will treat you for hypoglycemia if your blood sugar gets too low while you are in the hospital.

What are the complications associated with hyperosmolar hyperglycemic syndrome (HHS)?

HHS is a very serious medical condition. If it is not treated, it can lead to:

  • Seizures.
  • Coma.
  • Swelling of the brain.
  • Organ failure.
  • Death.

What can I do to relieve symptoms of hyperosmolar hyperglycemic syndrome (HHS)?

If you have symptoms of HHS, you should drink plenty of water and call 911 or go to the emergency room immediately. You will receive an IV with fluids and insulin to relieve your symptoms.


Can hyperosmolar hyperglycemic syndrome (HHS) be prevented?

The best way to prevent HHS is by following a healthy lifestyle and managing your diabetes. You should:

  • Check your blood sugar frequently to make sure you’re staying within your target range.
  • Take your insulin and other diabetes medications as directed by your doctor.
  • Follow a healthy diet.
  • Never drink alcohol on an empty stomach.
  • Get more rest and check your blood sugar more often when you are sick.
  • Know the symptoms of HHS and get help right away if you have any of them.

Outlook / Prognosis

What is the prognosis (outlook) for patients who have hyperosmolar hyperglycemic syndrome (HHS)?

The outlook for patients who have HHS largely depends on the person’s age, general health and how severe the disease is. Up to 20% of people who have HHS die from the condition.

If you’ve had HHS, you will need to work closely with your doctor once you are home from the hospital. You can reduce your risk of developing HHS again by controlling your diabetes and managing your diet and lifestyle.

Living With

When should I call my doctor about hyperosmolar hyperglycemic syndrome (HHS)?

HHS is a serious medical condition. If you have diabetes, you should call 911 or seek emergency medical help if you:

  • Ever have a blood sugar level over 400 mg/dL.
  • Are confused or disoriented.
  • Feel thirstier than usual.
  • Have to urinate more often than usual.
  • Have changes in your vision.
  • Feel weak or paralyzed anywhere in your body.

Last reviewed by a Cleveland Clinic medical professional on 11/13/2019.


  • Merck Manual Consumer Version. Hyperosmolar Hyperglycemic State (HHS). (https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/diabetes-mellitus-dm-and-disorders-of-blood-sugar-metabolism/hyperosmolar-hyperglycemic-state-hhs?query=Hyperosmolar%20Hyperglycemic%20State%20(HHS%29) Accessed 12/3/2019.
  • American Diabetes Association. Hyperosmolar Hyperglycemic Nonketotic Syndrome (HHNS). (http://www.diabetes.org/living-with-diabetes/complications/hyperosmolar-hyperglycemic.html) Accessed 12/3/2019.
  • Stoner GD. Hyperosmolar Hyperglycemic State. Am Fam Physician. 2017 Dec 1;96(11):729-736.
  • Diabetes.co.uk. Hyperosmolar Hyperglycemic Nonketotic Syndrome. (https://www.diabetes.co.uk/diabetes-complications/hyperosmolar-hyperglycemic-nonketotic-syndrome.html) Accessed 12/3/2019.

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