Understanding Hyperosmolar Hyperglycemic State (HHS)

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Quick Answer: What Is HHS?

Hyperosmolar hyperglycemic state (HHS) is a condition marked by very high blood glucose, often above 600 mg/dL, severe dehydration and changes in mental status. [1] It typically affects older adults with Type 2 diabetes and is often triggered by another illness, such as an infection. [1] The dehydration is profound and can lead to organ failure or coma without urgent treatment. [1]

What the research says

• About 1 in 5 people with HHS die, but the risk varies widely. A 2026 systematic review and meta-analysis of 27 studies (63,935 cases) found an overall mortality of 21.1%, ranging from 4.8% in North America to 40.0% in Africa. The median hospital stay was 7.5 days, and 40.8% of patients were admitted to intensive care (French et al., BMJ Open Diabetes Research & Care, 2026) [2].

• Illness and undiagnosed diabetes are common triggers. In the same analysis (median age 63.8 years), the most common precipitants were non-infective illness (49.5%), infection (44.0%) and a new diabetes diagnosis (31.7%); the figures overlap because some people had more than one. Complications included acute kidney injury (7.6%), pulmonary edema (4.8%) and acute coronary syndrome (3.9%) (French et al., BMJ Open Diabetes Research & Care, 2026) [2].

• Older age explains much of the high death rate. In a population-based study of 261,749 adults, 68 episodes of HHS in 66 patients were identified. Mortality was 19.0% at 1 month, 32.1% at 3 months and 35.7% at 12 months, compared with 4.8%, 6.3% and 9.4% in people with severe hyperglycemia without hyperosmolarity. After adjusting for age, the differences were no longer statistically significant (Kruljac et al., Experimental and Clinical Endocrinology & Diabetes, 2018) [3].

Key Takeaways

How does hyperosmolar hyperglycemic state (HHS) develop?

HHS develops slowly, from a combination of high blood sugar and not enough fluid. When blood sugar is high, the kidneys try to flush the extra glucose out in the urine. This takes a lot of water, so the body loses fluid quickly. [1]

Common Triggers

• Infections: among the most frequent triggers, with pneumonia, urinary tract infections (UTIs) and sepsis most often involved. Estimates range from about 44% of cases in a 2026 meta-analysis to 50% to 60% in Cleveland Clinic’s summary. [1] [2]

• Stopping diabetes medicines: skipping or stopping medicines can let blood sugar spiral. Cleveland Clinic reports this in about 21% of cases. [1]

• Acute illness: heart attack, stroke or pulmonary embolism can release stress hormones that raise blood sugar. [1]

• Certain drugs: corticosteroids, thiazide diuretics and some atypical antipsychotics can affect how the body handles carbohydrates and raise the risk of high blood sugar. [1]

• Undiagnosed diabetes: for some people, HHS is the first sign that they have Type 2 diabetes. [2]

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

Unlike other diabetes emergencies that develop within hours, HHS symptoms can take days or weeks to appear in full. [1]

Physical and Mental Signs

• Extreme thirst (polydipsia): an unquenchable need for water caused by severe dehydration. [1]

• Frequent urination: the body’s attempt to get rid of excess sugar. [1]

• Neurological changes: confusion, hallucinations, delirium, or weakness or paralysis that may be worse on one side of the body. [1]

• Vision problems: blurred vision or loss of vision. [1]

• Dryness: a very dry mouth and skin that is less elastic.

How is hyperosmolar hyperglycemic state (HHS) different from DKA?

Both conditions involve high blood sugar, but HHS and diabetic ketoacidosis (DKA) are different medical events.

What complications can hyperosmolar hyperglycemic state cause?

If it is not treated, the severe dehydration and concentrated blood of HHS can cause lasting damage.

• Seizures: caused by electrolyte imbalance and dehydration of the brain. [1]

• Coma: a state of prolonged unconsciousness. [1]

• Organ failure: particularly of the kidneys and heart.

• Cerebral edema: a rare but dangerous swelling of the brain that can occur if blood sugar is lowered too quickly during treatment. [1]

How is hyperosmolar hyperglycemic state (HHS) diagnosed?

Doctors diagnose HHS with a physical exam and blood tests. [1] The 2024 consensus report from the American Diabetes Association and other major diabetes societies sets out current criteria and treatment recommendations (Umpierrez et al., Diabetes Care, 2024) [4].

• Blood glucose test: a level over 600 mg/dL with low ketones points to HHS.

• Osmolality test: measures how concentrated the blood is; a high level shows severe dehydration.

• Ketone testing: blood or urine is checked to rule out DKA.

• Metabolic panel: checks electrolytes such as potassium and sodium, and kidney function.

How is hyperosmolar hyperglycemic state treated, and what is recovery like?

HHS must be treated in a hospital, and some patients need intensive care. [1] [2]

The Three Pillars of Treatment

1. Rehydration: large volumes of IV fluids restore blood volume and kidney function.

2. Electrolyte replacement: potassium and other minerals are replaced to prevent heart rhythm problems.

3. Insulin therapy: IV insulin gradually lowers blood sugar to a safe range. [1]

Managing the Trigger

Doctors also look for and treat the underlying cause, such as an infection or a heart problem, to help prevent another episode. [1]

Conclusion

Hyperosmolar hyperglycemic state is one of the most serious complications of diabetes, but it can often be prevented with steady blood sugar control and prompt treatment of illness. Knowing the slow-building signs of HHS can make the difference between a routine doctor’s visit and a life-threatening emergency.

Frequently Asked Questions

Can someone with Type 1 diabetes get HHS?

It is rare. HHS mostly affects people with Type 2 diabetes, while people with Type 1 diabetes are more prone to diabetic ketoacidosis (DKA).

Why is the mortality rate higher for HHS than DKA?

HHS often affects older adults who have other health conditions, and the dehydration is usually more severe. Cleveland Clinic reports mortality of about 10% to 20% for HHS and about 1% to 8% for DKA. [1]

Can you have HHS without a diagnosis of diabetes?

Yes. For some people, an episode of HHS is the first sign of Type 2 diabetes. In a 2026 meta-analysis, about 3 in 10 cases involved a new diabetes diagnosis. [2]

How long does it take to recover from HHS?

Hospital stays are often several days (the median was 7.5 days in a 2026 meta-analysis) [2], but full recovery can take weeks depending on severity and the underlying cause.

Does HHS cause a fruity breath smell?

No. That is a sign of DKA caused by ketones. HHS usually does not involve significant ketones.

Can drinking enough water prevent HHS?

Staying hydrated helps, but when blood sugar is very high you cannot drink enough water to make up for the fluid loss. Medical treatment is needed.

Is HHS painful?

HHS itself is not usually painful, but the triggers, such as a urinary tract infection or heart attack, can be.

Can stress cause HHS?

Severe physical stress, such as serious illness or surgery, is a common trigger. Emotional stress alone is unlikely to cause it.

What does “hyperosmolar” mean?

It means the blood has become very concentrated because so much water has been lost through urination. [1]

Can HHS cause a stroke?

HHS can mimic stroke symptoms, such as weakness on one side, and a stroke can also trigger HHS. Severe dehydration can also increase the risk of blood clots.

Is insulin always needed for HHS?

Yes. Insulin given by IV is a core part of treatment to bring the very high blood sugar down safely.

Why do symptoms develop so slowly?

People with Type 2 diabetes usually still make some insulin, so the body holds off a full emergency for longer than in Type 1. Dehydration builds up over days to weeks.

Can a high-sugar meal cause HHS?

A single meal is unlikely to cause it, but long-term poorly controlled blood sugar, especially with illness or missed medicine, can lead to HHS.

What are the long-term effects of HHS?

If treated promptly, many people recover fully. Severe cases can lead to lasting kidney or brain damage.

Can children get HHS?

It is rare, but it is being seen more often as Type 2 diabetes becomes more common in children and teenagers.

How often should I check my blood sugar to prevent HHS?

Follow your doctor’s advice, and check more often when you are sick or have an infection.

Can steroids cause HHS?

Yes. Corticosteroids raise blood sugar and can trigger HHS in people who are at risk. [1]

What is the difference between delirium and confusion?

Confusion is a general lack of clarity. Delirium is a more severe, sudden change in mental state that can include hallucinations.

Can HHS cause seizures?

Yes. Large shifts in blood concentration and electrolytes can trigger seizures.

Is HHS the same as a “diabetic coma”?

A coma is a possible result of untreated HHS, but the two are not the same thing.

What is a healthy blood sugar range?

For adults with diabetes, the American Diabetes Association’s general before-meal target is 80 to 130 mg/dL, but your doctor may set different targets for you.

Can I treat HHS at home?

No. HHS is a life-threatening emergency that needs IV fluids and close monitoring in a hospital. [1]

Does HHS affect the kidneys?

Yes. Severe dehydration can cause acute kidney injury. It occurred in 7.6% of cases in a 2026 meta-analysis. [2]

Can a heart attack trigger HHS?

Yes. The physical stress of a heart attack releases hormones that can cause a big rise in blood sugar. [1]

Why does HHS cause blurred vision?

Very high blood sugar changes the fluid balance in the eye’s lens, which changes its shape and affects focus.

Is HHS more common in the summer?

Heat can worsen dehydration, which may raise the risk of high blood sugar emergencies during hot weather, so extra care with fluids and monitoring is wise.

Can infections other than pneumonia cause HHS?

Yes. Any significant infection, including skin infections and dental abscesses, can be a trigger.

What is potassium’s role in HHS?

Insulin moves potassium into cells, which can lower blood levels dangerously, so potassium is carefully monitored and replaced during treatment.

Can HHS cause permanent brain damage?

Severe, prolonged dehydration or complications of treatment, such as brain swelling, can cause lasting damage, although this is uncommon.

How can I help someone who shows signs of HHS?

If a person with diabetes is confused, extremely thirsty or weak on one side, call emergency services or take them to the emergency room right away.

Can weight loss prevent HHS?

Keeping a healthy weight helps control Type 2 diabetes, which lowers the risk of HHS.

Does HHS cause a fever?

HHS does not, but the infection that triggered it often does.

Can I take my usual insulin dose if I suspect HHS?

Follow your sick-day plan and seek emergency care right away. Do not wait to see if it improves.

What is a sick-day plan?

It is a set of instructions from your doctor on how to manage your diabetes during illness to prevent complications such as HHS.

Can HHS cause low blood pressure?

Yes. Severe fluid loss reduces blood volume, which can cause dangerously low blood pressure (shock).

Is HHS more common in nursing homes?

It can be, because residents may have limited access to fluids or may not be able to tell others that they are thirsty.

Can HHS cause hallucinations?

Yes. Severe dehydration and metabolic imbalance can affect the brain and cause hallucinations.

Does HHS cause nausea?

It can, although nausea and vomiting are more typical of DKA.

Can I drive myself to the hospital if I suspect HHS?

No. Confusion and the risk of passing out make driving dangerous. Call emergency services.

What is osmolality?

It is a measure of how many particles, such as sugar and salt, are dissolved in the fluid part of your blood.

Can a urinary tract infection cause HHS?

Yes. Urinary tract infections are among the most common infection triggers. [1]

How do doctors know when HHS has resolved?

When blood sugar and blood concentration return to a safe range, dehydration is corrected and the person’s mental state is back to normal.

Can HHS cause one-sided weakness?

Yes. It can mimic a stroke by causing weakness or paralysis on one side of the body. [1]

Is HHS expensive to treat?

It often needs hospital and sometimes intensive care, so it is one of the more costly diabetes complications. About 4 in 10 patients in a 2026 meta-analysis were admitted to intensive care. [2]

Can I get HHS if I don’t have Type 2 diabetes?

It is very unlikely unless another medical condition causes extreme rises in blood sugar.

Does HHS cause dry skin?

Yes. Severe dehydration can make the skin dry and less elastic.

Can HHS cause a rapid pulse?

Yes. The heart beats faster to maintain blood pressure when fluid volume is low.

What is the first thing a doctor does for HHS?

Treatment usually starts with large-volume IV fluids to begin rehydrating the patient.

Can HHS happen again?

Yes. If diabetes is not well managed or another trigger occurs, a person can have more than one episode.

Is there a vaccine to prevent HHS?

No, but staying up to date with flu and pneumonia vaccines can help prevent infections that often trigger HHS.

Related Reading

Diabetic Ketoacidosis (DKA): Signs, Triggers, and What To Do in an Emergency explains the other major diabetes emergency and how it differs from HHS.

Hyperglycemia in Diabetes: Warning Signs, Target Numbers, and When It Becomes an Emergency explains high blood sugar warning signs and target ranges.

Dehydration: Symptoms, Causes, Risk Groups & Treatment — Complete Guide covers the signs and treatment of dehydration, a key feature of HHS.

Blood Glucose Test: Normal Blood Sugar Levels, Prediabetes and Diabetes Ranges explains how blood sugar is measured and what the results mean.

References

1. Cleveland Clinic. Hyperosmolar Hyperglycemic State (HHS). Cleveland Clinic. Last updated February 17, 2023. https://my.clevelandclinic.org/health/diseases/21147-hyperosmolar-hyperglycemic-state

2. French J, Bomphrey L, Manta A, et al. Hyperosmolar hyperglycaemic state: a systematic review and meta-analysis. BMJ Open Diabetes Res Care. 2026;14(3):e005765. PMID 42373194. https://doi.org/10.1136/bmjdrc-2025-005765

3. Kruljac I, Ćaćić M, Ćaćić P, et al. The impact of hyperosmolarity on long-term outcome in patients presenting with severe hyperglycemic crisis: a population based study. Exp Clin Endocrinol Diabetes. 2018;126(9):564-569. PMID 29165723. https://doi.org/10.1055/s-0043-117416

4. Umpierrez GE, Davis GM, ElSayed NA, et al. Hyperglycemic crises in adults with diabetes: a consensus report. Diabetes Care. 2024;47(8):1257-1275. PMID 39052901. https://doi.org/10.2337/dci24-0032

Disclaimer

This article is for informational purposes only and does not constitute medical advice. HHS is a life-threatening emergency. If you suspect someone has HHS, seek immediate medical attention.