What is Hyperglycemic Hyperosmolar Syndrome (HHS)?

Medically Reviewed By Kelly Wood, MD
Was this helpful?

Hyperglycemic hyperosmolar syndrome (HHS) is a serious and sometimes fatal complication of diabetes. It develops when a person’s blood sugar levels are excessively high for a long time. This leads to dehydration and a potentially altered mental state. HHS most commonly affects adults with type 2 diabetes. It is also known as hyperosmolar hyperglycemic nonketotic syndrome. People with HHS have extremely high blood sugar. However, they do not have Kussmaul breathing and ketones in the urine typically found with diabetic ketoacidosis (DKA).

Read on to learn more about the causes and symptoms of hyperglycemic hyperosmolar syndrome. This article also discusses treatments and outlook for people with HHS.

What are the causes of hyperglycemic hyperosmolar syndrome?

A child drinking water from his hand under a faucet
Dejan Ristovski/Stocksy United

HHS can occur when a person with diabetes experiences high blood sugar levels for an extended period of time.

Diabetes is a medical condition characterized by hyperglycemia, or high blood sugar. With this condition, the body has trouble producing or efficiently using insulin. Insulin is a hormone produced in the pancreas that helps the body use glucose from food.

In type 2 diabetes, the body makes enough insulin but has difficulty using it. This causes electrolytes, insulin and other hormones to build up in the blood. This can lead to dehydration when the body gets rid of extra glucose through urination.

Infections are one of the most common conditions leading to HSS. Hyperglycemia leading to HSS can also result from:

  • heart events, such as heart attack or stroke
  • undiagnosed diabetes
  • not following a diet designed for diabetes
  • respiratory conditions
  • circulatory conditions
  • certain medications
  • coexisting diseases
  • urinary conditions
  • substance abuse

Children and teenagers often develop HSS as the first sign of type 2 diabetes.

What are the symptoms of hyperglycemic hyperosmolar syndrome?

Symptoms of HHS may include:

  • lethargy
  • weakness
  • weak pulse
  • increased thirst
  • severe dehydration
  • dry skin and mouth
  • increased need to urinate
  • a general feeling of illness
  • low blood pressure, especially with position changes

If an infection is the cause of HHS, you may experience:

  • fever
  • rapid breathing
  • rapid heart rate

If a cardiac condition or event is the cause of HHS, you may also experience:

A 2017 study identified some of the most common neurological symptoms of HHS. They include coma, focal seizures, and atypical movements on one side of the body. Other neurological symptoms can include:

  • anxiety
  • confusion
  • difficulty seeing
  • trouble speaking or understanding
  • stroke-like symptoms such as weakness in a limb or one side of the face

How do doctors diagnose hyperglycemic hyperosmolar syndrome?

Distinguishing DKA from HHS can be challenging. However, doing so early is crucial for determining proper treatment.

To diagnose HHS, your doctor may examine your medical history, including details such as:

  • recent diet
  • symptoms
  • insulin regimen
  • current medications
  • onset of symptoms
  • missed doses of hypoglycemic medications
  • what was happening before symptoms began

Your doctor will then order a fingerstick to check your blood sugar level. A blood sugar level that indicates HHS is usually above 600 milligrams per decilitre (mg/dL).

To confirm a diagnosis, your doctor may also order other blood tests, such as:

  • electrolyte levels
  • hemoglobin A1C 
  • kidney function labs
  • arterial blood gasses
  • complete blood count

Doctors will also obtain a urine sample to test for glucose, ketones, and other chemical levels.

The higher the levels of electrolytes, glucose, and other hormones in your blood, the more acute the dehydration.

What are the treatments for hyperglycemic hyperosmolar syndrome?

Distinguishing HHS from DKA during diagnosis is crucial for determining proper treatment. Both conditions share similar symptoms, but their treatments are very different.

Rehydration with fluids is vital for someone with HHS. Delayed or inadequate treatment can result in a fast drop in glucose levels, altering the thickness of the blood. This may lead to complications such as blood clots or swelling in the brain.

During rehydration, your doctor will administer fluids promptly to gradually decrease glucose levels in the blood. They will aim to keep your blood glucose levels around 300 mg/dL. A nurse will then check your blood glucose levels every hour to ensure they are not dropping too fast. Your doctor may also administer frequent arterial blood gas tests.

Children and adolescents with HHS may need to receive fluids and electrolytes for up to 2 days. This can help prevent brain swelling.

Doctors and nurses will closely monitor your electrolyte levels and replace them as necessary. This includes monitoring levels of potassium, a critical electrolyte.

What is the outlook for someone with hyperglycemic hyperosmolar syndrome?

The outlook for someone with HHS depends on several factors, including:

  • age
  • degree of dehydration present
  • other medical conditions

Older adults with HHS that progresses to low blood pressure and a severe coma have a poorer outlook than younger people.

Researchers estimate that the mortality rate for adults who develop HHS is anywhere from 10–50%. This rate is potentially higher for children with HHS. These rates are much higher than for someone with DKA. This makes prompt diagnosis and treatment of HHS essential.

What are some potential complications of hyperglycemic hyperosmolar syndrome?

Complications of HHS can include:

  • Heart problems: This can be caused by dehydration.
  • Electrolyte imbalance: Low blood sugar can lead to electrolytes imbalances, such as low potassium.
  • Swelling in the brain: This is a rare but severe complication. It can occur if blood glucose levels and blood thickness drop too quickly. Brain swelling with HHS occurs more often in children and adolescents.

Can you prevent hyperglycemic hyperosmolar syndrome?

Preventing HHS mainly involves managing diabetes and staying hydrated. The following steps can help you prevent HHS:

  • Drink plenty of water.
  • Follow a strict diabetes-friendly diet.
  • Take insulin and other medications as prescribed by your doctor.

Other frequently asked questions

Here are some other common questions people ask about HHS. These answers were reviewed by Dr. Kelly Wood.

What is the difference between HHS and DKA?

HHS is characterized by severe hyperglycemia, or high blood sugar. DKA involves hyperglycemia and ketoacidosis. Ketoacidosis occurs when the body produces excess ketones, or blood acids.

Is HHS worse than DKA?

Although HHS is less common than DKA, it has a much higher mortality rate. Prompt diagnosis and treatment are essential for improving outcomes with HHS.


HHS is a condition that develops due to complications from diabetes. It usually occurs with type 2 diabetes and leads to increased blood thickness. This is due to excess electrolytes, glucose, and other hormones in the blood that the body cannot metabolize. It can result in severe dehydration.

Symptoms may include extreme thirst, weakness, or dry mouth or skin. In addition, people with HHS can experience confusion, weakness, or coma.

Contact your doctor if you have questions or concerns about the management or symptoms of diabetes.

Was this helpful?
Medical Reviewer: Kelly Wood, MD
Last Review Date: 2022 Oct 20
View All Diabetes Articles
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.