Diabetic Hyperglycemic Hyperosmolar Syndrome (HHS) is a serious complication of diabetes that happens when blood sugar levels get dangerously high and cause severe dehydration. It most often affects people with type 2 diabetes, especially older adults or those who are sick or unable to stay hydrated. Unlike diabetic ketoacidosis (DKA), HHS does not cause significant acid buildup in the body but can still be life-threatening if not treated quickly.

This guide explains what HHS is, how it develops, what symptoms to watch for, how doctors diagnose it, and what treatments can help. It also includes tips for prevention and long-term management.

Diabetic Hyperglycemic Hyperosmolar Syndrome (HHS), sometimes called hyperosmolar hyperglycemic state, occurs when very high blood sugar levels cause the body to lose a large amount of fluid. As dehydration worsens, the blood becomes thick and concentrated, which affects how the brain and other organs work.

In HHS, there is usually still some insulin in the body—enough to prevent fat from breaking down into ketones but not enough to keep blood sugar under control. Because it develops slowly, people may not realize how sick they are until serious symptoms appear.

HHS is less common than diabetic ketoacidosis but is more dangerous. It usually affects older adults with type 2 diabetes and other medical conditions.

• Accounts for less than 1% of hospital admissions for diabetes emergencies
• More frequent in people over age 60
• Mortality rate ranges from 10–20%, depending on how quickly treatment begins
• Common triggers include infection, heart attack, and certain medications

Early recognition and treatment significantly improve survival.

HHS often develops when something triggers a sudden spike in blood sugar or causes dehydration. It may take days or even weeks to appear. 

Common causes 

• Infections: such as pneumonia or urinary tract infections 

• Heart conditions: heart attack or stroke 

• Certain medications: steroids, diuretics, and some antipsychotics 

• Poor diabetes control: missed insulin doses or undiagnosed diabetes 

• Dehydration: due to vomiting, diarrhea, or limited fluid intake 

• Stress on the body: from surgery, injury, or illness 

Risk factors 

• Type 2 diabetes, especially if poorly controlled 

• Older age 

• Chronic illnesses or dementia 

• Limited access to water or medical care 

• Living alone or having difficulty recognizing symptoms 

Recognizing and managing these risks early can help prevent HHS. 

HHS doesn’t happen all at once—it builds over time. When insulin levels are too low for the body to use sugar properly, glucose builds up in the blood. The kidneys then try to get rid of the excess sugar by making more urine, which leads to large fluid losses. The more fluid that’s lost, the more dehydrated and concentrated the blood becomes. 

As dehydration worsens, the body’s salts (electrolytes) become unbalanced. This can affect the brain, causing confusion or even coma. Because the process happens gradually, people might not notice how serious it is until they are very ill. 

In short, HHS develops from a combination of high blood sugar, dehydration, and the body’s inability to balance fluids and electrolytes. 

The signs of HHS usually appear slowly, often over several days or weeks. Because symptoms can sneak up gradually, people may not realize how serious the situation is until they become very sick. 

Early warning signs 

• Feeling extremely thirsty and drinking more than usual 

• Urinating frequently 

• Feeling very tired or weak 

• Unexplained weight loss 

• Dry mouth or dry, cracked lips 

Worsening symptoms 

• Very dry skin and tongue 

• Rapid heartbeat and shallow breathing 

• Muscle cramps or body aches 

• Dizziness when standing up 

• Little or no urine despite feeling thirsty 

Severe symptoms (medical emergency) 

• Confusion, irritability, or unusual behavior 

• Trouble speaking or focusing 

• Extreme drowsiness or inability to stay awake 

• Seizures or jerking movements 

• Fainting or coma 

If you or someone you care for has diabetes and develops these symptoms—especially confusion, extreme thirst, or drowsiness—seek emergency medical care immediately. 

Because HHS develops slowly, many people don’t realize how sick they are until they arrive at the hospital. Doctors usually diagnose it based on symptoms, physical signs, and blood test results. 

What doctors look for 

• Symptoms: extreme thirst, frequent urination, confusion, or weakness 

• Signs of dehydration: dry mouth, dry skin, and low urine output 

• Vital signs: low blood pressure or fast heartbeat 

Tests used to confirm HHS 

• Blood sugar levels: typically extremely high (often over 600 mg/dL) 

• Blood chemistry: checks how concentrated your blood is and looks for electrolyte imbalances 

• Kidney function tests: high blood sugar and dehydration can strain the kidneys 

• Ketone test: little or no ketones are found, which helps distinguish HHS from DKA 

• Blood gases or pH test: to confirm there is no acid buildup 

Ruling out other causes 

Doctors may also check for infections, heart problems, or strokes that could have triggered the episode. Once HHS is confirmed, treatment begins right away. With quick care, most people recover fully. 

HHS is a medical emergency that always requires hospital treatment. The main goals are to safely lower blood sugar, restore lost fluids, and correct electrolyte imbalances. 

1. Rehydration 

Fluids are the first and most important part of treatment. Most people receive IV (intravenous) fluids to replace what was lost through urination and dehydration. This helps lower blood sugar naturally and improves circulation and kidney function. 

2. Insulin therapy 

Once the person is partially rehydrated, insulin is given through an IV to gently bring blood sugar back to a safe level. Lowering glucose too quickly can be dangerous, so doctors monitor levels closely and adjust treatment as needed. 

3. Correcting electrolytes 

Because large amounts of potassium and sodium are lost during dehydration, the care team checks and replaces these electrolytes to protect the heart and muscles. 

4. Treating the cause 

Infections, heart attacks, or certain medications can trigger HHS. Identifying and treating these underlying causes is essential to prevent it from happening again. 

5. Continuous monitoring 

During recovery, the medical team monitors blood sugar, electrolytes, and kidney function frequently to ensure treatment is working safely. 

With early treatment, most people make a full recovery, though some may need extra time to regain strength and hydration. 

HHS can cause serious complications if not treated quickly. These can result from both the illness itself and its treatment. 

Possible complications 

• Severe dehydration and shock 

• Kidney failure 

• Seizures or coma 

• Blood clots or stroke 

• Heart rhythm problems due to electrolyte imbalance 

• Rarely, brain swelling (cerebral edema) if blood sugar is lowered too quickly 

Prompt hospital care greatly reduces the risk of these complications. 

The outlook for HHS depends on how quickly it’s recognized and treated. 

• With early treatment, most people recover completely. 

• Older adults and those with heart or kidney problems may have a longer recovery time. 

• Untreated HHS can lead to coma or death, which is why recognizing the warning signs early is so important. 

Ongoing diabetes care, good hydration, and regular check-ups help prevent future episodes. 

Most cases of HHS can be prevented with proper diabetes management and awareness. 

• Monitor your blood sugar regularly. Follow your doctor’s plan for insulin or diabetes medications. 

• Stay hydrated. Drink plenty of water, especially during illness, hot weather, or travel. 

• Know the warning signs. Extreme thirst, frequent urination, and fatigue can signal dangerously high blood sugar. 

• Follow a sick-day plan. Check your blood sugar more often when you’re unwell and contact your healthcare provider if it stays high. 

• Treat infections promptly. Even minor illnesses can raise blood sugar levels quickly. 

• Review your medications. Some drugs can increase blood sugar—ask your doctor if your treatment needs adjustment. 

After recovering from HHS, preventing another episode becomes a key part of managing diabetes. 

• Follow up with your healthcare team to adjust medications and create a personalized diabetes plan. 

• Check your blood sugar regularly and record your results. 

• Stay hydrated every day, not just when you feel thirsty. 

• Eat balanced meals and include healthy carbohydrates and protein to maintain steady glucose levels. 

• Ask for help when you’re sick. Having someone check in can make it easier to manage your condition safely. 

Support from diabetes educators, nutritionists, and support groups can also make a big difference in helping you stay healthy and confident in your care. 

Diabetic Hyperglycemic Hyperosmolar Syndrome (HHS) is a serious but preventable emergency. It develops slowly, often when blood sugar remains high and dehydration worsens. The best defense is early recognition—knowing the symptoms, staying hydrated, and managing blood sugar every day. With proper education and medical care, people with diabetes can avoid HHS and live well. 

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