Hyperosmolar Hyperglycaemic State (HHS)

What is it?

Hyperosmolar Hyperglycaemic State (HHS) is a serious and potentially life-threatening condition linked to very high blood glucose levels. It happens when blood glucose rises over time and the body becomes severely dehydrated. Unlike diabetic ketoacidosis (DKA), HHS usually develops more slowly — often over several days. HHS most often affects people living with type 2 diabetes, but it can happen to anyone whose blood glucose levels remain very high for a prolonged period.

What’s happening in the body?

When blood glucose levels stay very high:

• The body tries to remove excess glucose through urine
• This leads to large fluid losses (dehydration)
• The blood becomes more concentrated (hyperosmolar)
• The brain and other organs are affected by this fluid imbalance

Because this develops gradually, it can sometimes go unnoticed until someone becomes very unwell.

Signs and symptoms to look out for

HHS can build up over time. Common signs include:

• Very high blood glucose levels (often above 30 mmol/L)
• Extreme thirst
• Passing large amounts of urine
• Dry mouth and dry skin
• Feeling very tired or weak
• Blurred vision

As it progresses, symptoms may include:

• Confusion or difficulty thinking clearly
• Drowsiness
• Changes in behaviour
• Seizures or loss of consciousness (in severe cases)

If someone is showing signs of confusion or reduced awareness, this is a medical emergency.

What can lead to HHS?

HHS often develops when something else is going on in the body. Common triggers include:

• Infection (such as chest or urinary infections)
• Not taking diabetes medication as prescribed
• New diagnosis of diabetes
• Other illnesses or stress on the body
• Some medications (such as steroids)

It’s important to remember this is not about blame — HHS is usually the result of multiple factors coming together.

When to seek help

You should seek urgent medical advice if:

• Blood glucose levels remain very high and are not coming down
• You are unable to keep fluids down
• You feel increasingly unwell, drowsy, or confused

Call emergency services if someone is difficult to wake, very confused, or unconscious.

How is HHS treated?

HHS is treated in hospital and usually involves:

• Careful rehydration with intravenous fluids
• Insulin to gradually reduce blood glucose levels
• Monitoring and correcting electrolyte levels
• Treating any underlying cause (such as infection)

With prompt treatment, many people recover well.

Reducing the risk

There are ways to lower the risk of HHS:

• Checking blood glucose levels more often when unwell
• Staying well hydrated
• Following your diabetes sick day plan (if you have one)
• Seeking early advice if levels are rising or you’re unsure what to do

If you don’t yet have a sick day plan, your healthcare team can help you create one that works for you.

>> Download Sick Day Plan template

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Last updated: March 2026

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TYPE 2 DIABETES
Living with Type 2 Diabetes
Causes of Type 2 Diabetes
Insulin Resistance
Prediabetes
Type 2 Diabetes Remission
Managing Type 2 Diabetes
Food Choices for Type 2’s
Weight Loss
Medications for Type 2 Diabetes
Blood Glucose Monitoring for Type 2’s
Starting on Insulin
Hyperosmolar Hyperglycaemic State (HSS)
Low Blood Glucose Levels - Hypoglycaemia
Type 2 Diabetes in Children and Young People

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