Hyperosmolar hyperglycemic state (HHS) is a life-threatening emergency affecting predominantly older adults with type 2 diabetes. It features blood glucose typically above 600 mg/dL, severe dehydration (often 8 to 12 liters of total body fluid deficit), profound hyperosmolality (greater than 320 mOsm/kg), and altered mental status — but minimal ketosis. Mortality is 5 to 20 percent. The most common triggers are infection, missed medications, and new diabetes presentation. Treatment requires ICU-level care with aggressive fluids, insulin infusion, electrolyte repletion, and management of the trigger. Prevention centers on glucose monitoring, sick-day plans, and prompt infection treatment.
What HHS Is
- A relative insulin deficiency state. Enough insulin remains to suppress lipolysis and ketogenesis, but not enough to control glucose
- Glucose-driven osmotic diuresis. Sustained extreme hyperglycemia produces massive urinary glucose loss with associated water and electrolyte loss
- Severe dehydration. Total body water deficit often 8 to 12 liters, sometimes more
- Hyperosmolality. Serum osmolality typically greater than 320 mOsm/kg, leading to cellular dehydration in the brain and altered mental status
- Slow onset. Days to weeks, unlike the hours-to-days timeline of DKA
Diagnostic Criteria
| Parameter | HHS Criteria |
|---|---|
| Plasma glucose | Greater than 600 mg/dL (usually 600 to 1,200) |
| Serum osmolality | Greater than 320 mOsm/kg (effective) |
| Arterial pH | Greater than 7.30 (no significant acidosis) |
| Serum bicarbonate | Greater than 18 mEq/L |
| Serum/urine ketones | Negative or small only |
| Anion gap | Variable; usually normal or mildly elevated |
| Mental status | Stupor or coma in many; alterations common in all |
HHS vs DKA
| Feature | HHS | DKA |
|---|---|---|
| Typical patient | Older, type 2 diabetes | Younger, type 1 diabetes (also type 2 in some cases) |
| Onset | Days to weeks | Hours to days |
| Glucose | Greater than 600 mg/dL | 250 to 600 mg/dL usually |
| Ketones | Negative or trace | Moderate to large |
| pH | Greater than 7.30 | Less than 7.30 |
| Bicarbonate | Greater than 18 mEq/L | Less than 18 mEq/L |
| Osmolality | Greater than 320 mOsm/kg | Variable, often less than 320 |
| Fluid deficit | Severe — 8 to 12 liters typical | Moderate — 3 to 6 liters typical |
| Mental status | Often markedly altered | Often preserved until very late |
| Mortality | 5 to 20 percent | Less than 5 percent |
See our companion piece on DKA symptoms for the parallel emergency in type 1 diabetes.
Causes and Triggers
Most Common Triggers
- Infection — accounts for 30 to 60 percent of cases; urinary tract infection and pneumonia are the leading specific infections
- Medication non-adherence — especially insulin and oral diabetes drugs; common in elderly with cognitive impairment
- New diabetes presentation — about 7 to 17 percent of cases are in previously undiagnosed patients
- Cardiovascular events — myocardial infarction, stroke
- Gastrointestinal events — pancreatitis, GI bleeding, severe diarrhea
- Surgery and trauma
Medication Triggers
- Corticosteroids (especially high-dose, IV pulses)
- Atypical antipsychotics (olanzapine, clozapine, quetiapine)
- Thiazide and loop diuretics
- Beta-blockers in some patients
- Phenytoin
- Calcineurin inhibitors
- Sympathomimetics
- Total parenteral nutrition
Social and Functional Factors
- Cognitive impairment that limits self-care and water intake
- Limited mobility
- Limited access to fluids (residential care, heat waves, restricted intake)
- Social isolation that delays recognition
Clinical Presentation
Early Symptoms (Days to Weeks)
- Increased thirst and urination
- Weight loss
- Weakness and fatigue
- Leg cramps
- Blurred vision
- Subtle mental status changes
Established HHS
- Severe dehydration — dry mucous membranes, sunken eyes, poor skin turgor, tachycardia, hypotension
- Altered mental status — ranging from confusion to coma
- Focal neurologic signs in 20 to 25 percent — can mimic stroke (hemiparesis, aphasia, seizures)
- Hyperthermia or signs of underlying infection
- Cool extremities, weak pulses
- Tachypnea (more shallow than the deep Kussmaul breathing of DKA)
- Glucose extremely high on point-of-care testing
Initial Workup
- Vital signs, mental status, dehydration assessment
- Point-of-care glucose; venous blood for full panel
- Basic metabolic panel — glucose, sodium, potassium, BUN, creatinine, bicarbonate, anion gap
- Magnesium, phosphate, calcium
- Arterial or venous blood gas
- Serum ketones (beta-hydroxybutyrate) and urine ketones
- CBC with differential
- Calculated effective serum osmolality: 2 × Na + glucose/18
- Corrected sodium for hyperglycemia: measured Na + 1.6 × (glucose – 100)/100
- ECG — rule out MI, assess for hyperkalemia changes
- Chest X-ray, urinalysis with culture — most common infection sources
- Other cultures based on clinical exam
- Cardiac enzymes if any concern for MI
- CT head if focal neurologic deficits or unclear cause of altered mentation
Treatment Principles
Fluid Resuscitation — The Cornerstone
- Initial bolus 1 to 1.5 liters of isotonic saline (0.9 percent) in the first hour
- Continue isotonic saline at 250 to 500 mL/hour, adjusting based on hemodynamics
- Switch to 0.45 percent saline once volume is restored and corrected sodium is normal or high
- Goal: replace half the deficit in the first 12 hours, the remainder over the next 12 to 24 hours
- Total replacement often 8 to 12 liters or more
- Switch to D5 (5 percent dextrose) containing fluids once glucose reaches around 300 mg/dL
- Watch for cerebral edema (rare in adults but possible), fluid overload in cardiac or renal patients
Insulin Infusion
- Start insulin only after initial fluid resuscitation has begun (some patients improve substantially with fluids alone)
- Initial rate is lower than for DKA — typically 0.05 to 0.1 units/kg/hour
- Target glucose reduction of 50 to 100 mg/dL per hour to avoid overly rapid osmotic shifts
- Once glucose reaches 250 to 300 mg/dL, reduce insulin and add dextrose to IV fluids
- Continue insulin until mental status, osmolality, and hyperglycemia have resolved
- Transition to subcutaneous insulin with overlap when stable and tolerating oral intake
Potassium and Electrolyte Repletion
- Most HHS patients have a total body potassium deficit (3 to 5 mEq/kg) even if initial serum K+ is normal or elevated
- Hold insulin if K+ is less than 3.3 mEq/L until corrected — insulin drives potassium into cells and can cause severe hypokalemia
- Add 20 to 40 mEq KCl per liter of IV fluid once K+ is 3.3 to 5.0 and urine output is adequate
- Phosphate may need repletion if severely low and symptomatic
- Magnesium often needs repletion
- Calcium monitoring
Underlying Cause
- Identify and treat the trigger — most importantly infection
- Empiric antibiotics if infection is suspected and the source not yet identified, especially in immunocompromised or septic patients
- Cardiac, neurologic, and other workup as indicated
- Review home medication list — adjust HHS-triggering drugs
Monitoring
- Hourly point-of-care glucose
- Electrolytes every 2 to 4 hours initially
- Frequent neurologic checks
- Strict input and output
- Continuous cardiac monitoring
- ICU-level care in most cases
Complications
- Hypovolemic shock if fluid resuscitation is delayed
- Acute kidney injury — often present on arrival; usually improves with fluids
- Thromboembolism. Hypercoagulable state; consider prophylactic anticoagulation
- Cerebral edema. Rare in adults but possible with too-rapid correction; more concerning in children and adolescents
- Rhabdomyolysis. From prolonged immobility and hyperosmolality; check CK
- Cardiovascular events. MI, arrhythmia, stroke
- Hospital-acquired infections in the ICU course
- Refeeding syndrome if severely malnourished
Prognosis
- Mortality 5 to 20 percent — higher than DKA
- Worse outcomes with older age, severe altered mental status on arrival, very high osmolality, multiple comorbidities, and major precipitating events (MI, stroke, sepsis)
- Survivors often have prolonged hospital and rehabilitation stays
- Functional decline after HHS is common in elderly patients
Prevention
| Strategy | Details |
|---|---|
| Glucose monitoring | Routine home checks; CGM for selected high-risk patients |
| Sick-day plan | Written instructions: when to check more often, when to call the team, hydration goals, medication adjustments |
| Infection treatment | Prompt evaluation and treatment of UTI, pneumonia, skin/soft tissue infections in older adults with diabetes |
| Medication adherence | Pill organizers, simplified regimens, caregiver involvement for cognitive impairment |
| Caregiver education | Recognize early symptoms — increased thirst, urination, confusion — and have a low threshold to seek care |
| Vaccinations | Influenza, pneumococcal, COVID, RSV (per current recommendations) |
| Heat exposure | Hydration in hot weather; check on isolated elderly patients during heat waves |
| High-risk medication review | Monitor patients on corticosteroids, atypical antipsychotics, thiazides more closely |
| Avoid sugary beverages during illness | Patients with nausea sometimes drink soda or juice to maintain calories; this worsens hyperglycemia |
Warning Signs — When to Call or Go to the ER
- Persistent glucose above 300 mg/dL — call the team
- Glucose above 400 to 500 mg/dL with any symptoms — emergency evaluation
- Confusion, lethargy, or new neurologic symptoms in a person with diabetes
- Severe thirst, dry mouth, decreased urination
- Inability to keep down fluids during illness
- Signs of infection plus high glucose
- Family or caregiver noticing personality, alertness, or speech changes
Related Reading
See DKA symptoms for the related emergency in type 1 diabetes, hyperglycemia vs hypoglycemia symptoms, the complications hub, and the ADA 2024 Standards of Care for authoritative clinical guidance.
The Bottom Line
Hyperosmolar hyperglycemic state is the most dangerous hyperglycemic emergency in type 2 diabetes — characterized by glucose above 600 mg/dL, severe dehydration of 8 to 12 liters or more, profound hyperosmolality, and altered mental status, but with minimal ketosis. It develops slowly over days to weeks, most often triggered by infection, missed medications, or a new presentation of diabetes. Mortality is 5 to 20 percent, mostly because of age and comorbidities. Treatment requires ICU-level fluid resuscitation, careful insulin infusion, electrolyte repletion, and management of the underlying cause. Prevention is highly effective — glucose monitoring, sick-day plans, prompt infection treatment, caregiver education, and medication adherence prevent most cases. Anyone with diabetes who has persistent very high glucose, severe thirst, decreased urination, or any confusion or lethargy should seek emergency care immediately.
