Hyperosmolar Hyperglycemic State (HHS)

What happens in HHS

When insulin is not working well enough, blood sugar rises. The kidneys try to remove the excess glucose in urine, taking large amounts of water and salts with it. If the person cannot drink enough to keep up, often because they are older, unwell or have reduced thirst, they become severely dehydrated. Blood sugar climbs further and the blood becomes very concentrated (high osmolality). Water is drawn out of brain cells, causing confusion and coma.

Unlike diabetic ketoacidosis (DKA), people with HHS usually still make enough insulin to prevent major ketone production, so the blood does not become very acidic. HHS develops more slowly, over days to weeks, and dehydration is often much more severe. Overlapping cases with features of both occur.

HHS vs DKA

Causes and triggers

• Infections: the most common trigger, especially pneumonia and urinary tract infections
• Missed or stopped diabetes medicines or insulin
• Undiagnosed type 2 diabetes: HHS can be the first sign
• Medicines that raise blood sugar or cause fluid loss: steroids, thiazide diuretics, some antipsychotics
• Acute illness: stroke, heart attack, pancreatitis, trauma or surgery
• Reduced fluid intake: older adults with reduced thirst, dementia, immobility or living alone
• Sugary drinks consumed in large amounts during illness
• Alcohol or drug misuse

Symptoms

Symptoms develop gradually:

• extreme thirst and dry mouth
• frequent, large amounts of urine at first, then reduced urine as dehydration worsens
• weakness, tiredness and leg cramps
• blurred vision
• weight loss
• warm, dry skin
• confusion, disorientation and drowsiness
• hallucinations, slurred speech or weakness on one side, which can mimic stroke
• seizures
• coma

Diagnosis

Key hospital tests include:

• Blood glucose: usually above 600 mg/dL (33.3 mmol/L)
• Serum osmolality: above about 320 mOsm/kg
• Ketones and blood gas: little or no ketones; pH usually above 7.3
• Electrolytes and kidney function: sodium, potassium and creatinine (kidney injury is common)
• Tests for the trigger: blood and urine cultures, chest X-ray, ECG, cardiac enzymes, brain imaging if needed

Treatment

HHS is treated in hospital, often in intensive or high-dependency care:

1. IV fluids: the most important step. Large volumes are given carefully over 24 to 48 hours to restore circulation and gradually lower sugar and osmolality. Correcting too quickly can cause brain swelling.
2. Insulin: given by IV infusion, usually after fluids have started lowering glucose.
3. Potassium and other electrolytes: replaced as levels are monitored closely.
4. Treating the trigger: antibiotics for infection, treatment of stroke or heart attack.
5. Preventing blood clots: HHS thickens the blood, so blood thinners are usually given.
6. Monitoring: for kidney injury, heart rhythm problems and pressure sores.

Complications and outlook

HHS is serious, with a higher death rate than DKA, largely because it affects older people with other illnesses and because of the triggering condition. Complications include blood clots (stroke, heart attack, deep vein thrombosis), acute kidney injury, seizures, brain swelling and pressure injuries. Most people who are treated promptly recover fully.

Prevention

• Check blood sugar regularly, and more often when unwell.
• Follow a written sick day plan: keep drinking sugar-free fluids, keep taking diabetes medicines unless advised otherwise, check sugar every 2 to 4 hours, and know when to call your care team.
• Ensure older adults with diabetes have easy access to fluids, especially in hot weather or illness.
• Watch for early signs of infection and treat them promptly.
• Review medicines that raise blood sugar.
• Have regular diabetes checkups and HbA1c tests.

Frequently asked questions

What is hyperosmolar hyperglycemic state?

HHS is a dangerous complication of diabetes, usually type 2, in which blood sugar becomes extremely high and the body becomes severely dehydrated. It causes thirst, frequent urination, confusion and can lead to coma. It needs emergency treatment.

What is the difference between HHS and DKA?

HHS causes extremely high blood sugar and severe dehydration with little or no ketones, develops over days to weeks, and mainly affects older adults with type 2 diabetes. DKA develops faster, causes acid build-up from ketones, and is more common in type 1 diabetes.

What blood sugar level causes HHS?

HHS usually involves blood sugar above 600 mg/dL (33.3 mmol/L), often much higher. A glucose meter may simply read "HI". Any reading this high, especially with confusion or drowsiness, needs emergency care.

Can HHS happen in people without known diabetes?

Yes. HHS can be the first sign of type 2 diabetes, particularly in older adults who have had unrecognized high blood sugar for some time. Extreme thirst, frequent urination and confusion should prompt a blood sugar check.