Hemolytic uremic syndrome (HUS): symptoms, causes, treatment and recovery

Hemolytic uremic syndrome (HUS) is a serious condition that can develop when tiny blood vessels become damaged, causing red blood cells to break down, platelets to fall and the kidneys to become injured. It is particularly important to recognise HUS after an episode of diarrhea, especially bloody diarrhea.

The condition is most commonly associated with Shiga toxin-producing Escherichia coli (STEC), but HUS can also develop because of other infections, certain medicines, autoimmune conditions, pregnancy, cancer or abnormalities involving the immune system and complement pathway.

HUS is a medical emergency because kidney function can deteriorate rapidly. The good news is that, with prompt medical care, many people recover, particularly those with typical HUS following an E. coli infection. However, some people can develop long-term kidney, blood pressure, neurological or other complications.

What is hemolytic uremic syndrome?

Hemolytic uremic syndrome is a type of thrombotic microangiopathy, a group of disorders in which small blood vessels become damaged and develop microscopic blood clots.

The name describes three major features:

• Hemolytic: red blood cells are destroyed faster than the body can replace them.
• Uremic: kidney injury can prevent the body from adequately removing waste products from the blood.
• Syndrome: several related abnormalities occur together rather than there being a single symptom.

The classic triad of HUS is microangiopathic hemolytic anemia, thrombocytopenia and acute kidney injury.

HUS is most common in young children, particularly those under 5 years of age, but adults can develop it as well. In adults, the disease may sometimes cause more prominent neurological complications.

What causes hemolytic uremic syndrome?

The most common cause is an infection with Shiga toxin-producing E. coli (STEC). These bacteria produce Shiga toxin, which can damage the lining of small blood vessels and trigger the chain of events that causes HUS.

STEC can be transmitted through contaminated food or water, undercooked meat, unpasteurised dairy products, contaminated fruits or vegetables, contaminated recreational water and contact with infected people or animals.

Other causes include:

• Shigella dysenteriae, particularly Shiga toxin-producing strains
• Streptococcus pneumoniae
• Certain other bacterial or viral infections
• Some chemotherapy and other medicines
• Autoimmune diseases
• Pregnancy-related complications
• Cancer
• Severe hypertension
• Genetic abnormalities affecting complement regulation

When HUS is caused by uncontrolled activation of the complement system, it is commonly referred to as atypical HUS (aHUS). It may be triggered by infection, pregnancy, medication or another stress on the body in people with an underlying genetic or acquired susceptibility.

Which bacteria may cause hemolytic uremic syndrome?

The bacteria most strongly associated with HUS are:

1. Shiga toxin-producing E. coli (STEC) – the leading cause of typical HUS.
2. Shigella dysenteriae – particularly Shiga toxin-producing strains.
3. Streptococcus pneumoniae – an uncommon cause of HUS, usually associated with severe pneumococcal infection such as pneumonia or meningitis.

Other infectious organisms have occasionally been associated with HUS or related thrombotic microangiopathies.

What are the symptoms of hemolytic uremic syndrome?

HUS symptoms can change as the condition progresses. The illness may initially look like gastroenteritis before signs of blood-cell destruction and kidney injury appear.

What are the 5 symptoms of hemolytic uremic syndrome?

Five important symptoms to watch for are:

1. Bloody diarrhea, particularly when HUS follows an E. coli infection
2. Reduced urine output or very little/no urine
3. Pale skin, often caused by anemia
4. Extreme tiredness or weakness
5. Easy bruising or tiny red spots on the skin caused by a low platelet count

Other symptoms can include abdominal pain, vomiting, headache, swelling of the feet or ankles, blood in the urine, high blood pressure, confusion, irritability, seizures and reduced alertness.

Not everyone with HUS has bloody diarrhea. Atypical HUS, for example, may develop without a preceding diarrhoeal illness.

These symptoms reflect the systemic nature of the disease, which affects the kidneys, brain, and other organs.

How long does it take for HUS to develop?

When HUS follows STEC infection, the diarrhoeal illness generally begins a few days after exposure. HUS usually develops about 3 to 10 days after the onset of diarrhoea, although the exact timing varies. StatPearls reports a median onset of approximately 6.5 to 7 days after diarrhoea begins.

This is why a child or adult who appears to be recovering from bloody diarrhoea can become unwell again several days later.

A particularly important warning pattern is:

Diarrhoea → apparent improvement → reduced urination, pallor, unusual tiredness, bruising or swelling.

These changes require urgent medical assessment.

What does HUS feel like?

There isn’t one single way HUS feels. In typical HUS, a person may initially experience severe stomach cramps, diarrhoea, vomiting and sometimes fever.

As anemia and kidney injury develop, they may feel unusually tired, weak, pale, dizzy or short of breath. Headache can occur, and some people develop swelling because the kidneys are struggling to remove excess fluid.

More serious HUS can cause confusion, unusual sleepiness, seizures or reduced awareness. These neurological symptoms require emergency treatment.

How do I know if I have HUS?

Symptoms alone cannot confirm HUS. A healthcare professional usually looks for the characteristic combination of anemia, low platelets and kidney injury and then investigates the underlying cause.

Testing may include:

• Complete blood count to check hemoglobin and platelets
• Kidney function tests, including creatinine and estimated GFR
• Electrolytes
• Blood tests for hemolysis, such as LDH, bilirubin and haptoglobin
• Peripheral blood smear to look for fragmented red blood cells called schistocytes
• Urine testing
• Stool testing for Shiga toxin or STEC when diarrhoea is present
• ADAMTS13 testing when TTP needs to be excluded
• Complement testing and, when appropriate, genetic testing for suspected aHUS

HUS can resemble other serious conditions, particularly thrombotic thrombocytopenic purpura (TTP), so accurate diagnosis is essential because treatment differs.

What is the triad of HUS?

The classic triad of HUS is:

1. Microangiopathic hemolytic anemia
Red blood cells are mechanically damaged as they pass through injured small blood vessels.

2. Thrombocytopenia
The platelet count falls because platelets become involved in the formation of microscopic blood clots.

3. Acute kidney injury
Damage to small blood vessels in the kidneys reduces their ability to filter blood effectively.

This triad is one of the most important clinical clues to HUS.

How is hemolytic uremic syndrome typically treated?

Treatment depends heavily on the type and cause of HUS.

Typical HUS caused by STEC

There is no specific antibiotic that routinely cures STEC-associated HUS. Treatment is primarily supportive, often in a hospital.

Management may include:

• Careful fluid and electrolyte management
• Monitoring urine output and kidney function
• Blood transfusions when necessary
• Management of high blood pressure
• Treatment of complications
• Dialysis if the kidneys cannot adequately remove waste or fluid

Early appropriate fluid management during STEC diarrhoeal illness may reduce the risk of severe kidney injury.

Atypical HUS

Atypical HUS requires a different approach. Complement inhibition, particularly with medicines such as eculizumab or ravulizumab, may be used to control abnormal complement activation. Treatment should be started promptly when aHUS is strongly suspected because delaying therapy can increase the risk of serious kidney and other organ damage.

HUS caused by other infections

The underlying infection may need specific treatment. For example, pneumococcal-associated HUS requires treatment of the underlying pneumococcal infection. HUS associated with Shiga toxin-producing Shigella also requires specialist management.

Do you give antibiotics for HUS?

Not routinely.

If HUS is caused by STEC, antibiotics are generally avoided because antimicrobial treatment may increase the risk of developing HUS or worsen outcomes. The CDC specifically advises against antibiotics for STEC infection.

However, this does not mean that antibiotics are never used in a person with HUS. Certain bacterial infections, including pneumococcal infection and some Shigella infections, may require antibiotic treatment.

Therefore, antibiotics should never be started or stopped without medical advice when HUS or STEC infection is suspected.

Anti-diarrhoeal medicines that slow intestinal movement should also be avoided in suspected STEC infection, particularly when bloody diarrhoea is present.

Can kidneys recover from HUS?

Yes. Kidneys can recover after HUS, particularly when the condition is recognised and treated promptly.

Many people with typical HUS recover kidney function over a period of weeks. Some patients may temporarily require dialysis while the kidneys recover. The CDC notes that most people with HUS recover within a few weeks, although some develop permanent health problems.

Recovery is not always complete. Long-term complications can include:

• High blood pressure
• Protein in the urine
• Reduced kidney function
• Chronic kidney disease
• Neurological complications

StatPearls reports that up to 25% of patients may develop long-term renal consequences after typical HUS.

For this reason, follow-up kidney function and blood pressure checks can remain important even after a person feels completely well.

What are the four warning signs of a damaged kidney?

Kidney disease can be silent, so symptoms alone cannot reliably detect early kidney damage. However, four important warning signs are:

1. A change in urination, including urinating much less or more than usual
2. Swelling, particularly around the ankles, feet, legs or eyes
3. Blood or persistent foam in the urine
4. Unusual tiredness, weakness or difficulty concentrating

These symptoms have many possible causes and do not automatically mean that the kidneys are damaged. Blood and urine testing is needed to assess kidney function properly.

In HUS specifically, a sudden reduction in urine output after diarrhoea is particularly concerning.

What are the common symptoms of uremia?

Uremia occurs when waste products build up in the blood because kidney function is severely impaired.

Symptoms can include:

• Nausea and vomiting
• Loss of appetite
• Extreme tiredness
• Difficulty concentrating
• Confusion
• Itching
• Muscle cramps
• Sleep problems
• A metallic or unpleasant taste
• Shortness of breath
• Swelling

Severe uremia can affect the brain and other organs and requires urgent medical treatment.

It is important to remember that not everyone with HUS develops uremia. Uremia is a consequence of significant kidney failure rather than a defining symptom of every case of HUS.

What is the survival rate of HUS?

There is no single survival rate that applies to every form of HUS.

For typical HUS, the prognosis is generally favourable with timely supportive treatment. StatPearls estimates overall mortality for typical HUS at around 5%, which corresponds to survival of approximately 95%, although individual outcomes can vary considerably.

The outcome depends on factors such as age, the underlying cause, severity of kidney injury, neurological involvement and whether serious complications develop.

Atypical HUS is different and historically carried a higher risk of kidney failure and death, particularly when untreated. Modern complement-targeted treatment has substantially changed the outlook for many patients with aHUS.

How can hemolytic uremic syndrome be prevented?

There is no way to prevent every type of HUS because some forms are linked to genetics, autoimmune disease, medicines or other medical conditions.

However, many cases of infection-associated HUS can be reduced by preventing STEC infection.

Important precautions include:

• Cook meat thoroughly.
• Avoid unpasteurised milk and other unpasteurised dairy products.
• Wash hands thoroughly after using the toilet and changing nappies and before preparing food.
• Keep raw meat separate from ready-to-eat food.
• Clean kitchen surfaces and utensils properly.
• Wash fruits and vegetables appropriately.
• Avoid swallowing water from potentially contaminated pools, lakes or other recreational water.
• Do not prepare food for others while experiencing diarrhoea.
• Follow safe food-storage practices.

The CDC and Mayo Clinic also recommend avoiding anti-diarrhoeal medicines in suspected STEC infection and seeking medical advice promptly for bloody diarrhoea.

When should you seek medical help?

HUS can progress quickly, so certain symptoms should never be ignored.

Seek urgent medical care if diarrhoea, particularly bloody diarrhoea, is followed by:

• Very little or no urine
• Blood in the urine
• Unusual bruising or tiny red spots
• Pale skin
• Severe tiredness or weakness
• Swelling
• Confusion or reduced alertness
• Seizures
• Difficulty breathing

The CDC considers HUS a medical emergency and recommends immediate medical attention when these warning signs appear.

For children, parents should be especially alert because children under 5 are at increased risk of HUS following STEC infection.

Frequently asked questions about hemolytic uremic syndrome

What are the 5 symptoms of hemolytic uremic syndrome?

Five important symptoms are bloody diarrhoea, reduced urine output, pale skin, extreme tiredness and easy bruising or tiny red spots. Other symptoms include abdominal pain, vomiting, headache, swelling, blood in the urine and, in severe cases, confusion or seizures.

How long does it take for HUS to develop?

With typical STEC-associated HUS, the syndrome usually develops 3 to 10 days after diarrhoea begins, with the median reported onset around 6.5 to 7 days.

What is the triad of HUS?

The classic triad is microangiopathic hemolytic anemia, thrombocytopenia and acute kidney injury.

What causes hemolytic uremic syndrome?

The most common cause is Shiga toxin-producing E. coli. Other causes include Shigella dysenteriae, Streptococcus pneumoniae, certain medicines, infections, autoimmune conditions, pregnancy-related complications and genetic or acquired abnormalities affecting complement regulation.

Can kidneys recover from HUS?

Yes. Many patients recover kidney function, sometimes after temporarily requiring dialysis. However, some develop persistent proteinuria, high blood pressure or reduced kidney function, so follow-up is important.

What are the four warning signs of a damaged kidney?

Four useful warning signs are changes in urination, swelling, blood or persistent foam in the urine, and unexplained fatigue or weakness. Early kidney disease may cause no symptoms, so blood and urine testing is more reliable than symptoms alone.

What is the survival rate of HUS?

Typical HUS has a generally good prognosis with appropriate care. StatPearls estimates mortality at around 5% for typical HUS, but survival varies according to the cause and severity. aHUS has a different prognosis and requires rapid specialist treatment.

How do I know if I have HUS?

You cannot confirm HUS based on symptoms alone. Doctors typically use blood counts, kidney function tests, tests for hemolysis, a peripheral blood smear, urine testing and, when appropriate, stool testing for Shiga toxin. Other tests may be needed to distinguish HUS from TTP and other conditions.

What are the common symptoms of uremia?

Uremia can cause nausea, vomiting, loss of appetite, severe fatigue, itching, muscle cramps, difficulty concentrating, confusion, sleep problems and shortness of breath. It generally occurs when kidney function has become severely impaired.

Do you give antibiotics for HUS?

Antibiotics are not routinely given for STEC-associated HUS and can increase the risk of HUS when used during STEC infection. Some other bacterial causes of HUS require antibiotics, so treatment depends on identifying the underlying infection.

How is HUS typically treated?

Typical HUS is mainly treated with supportive hospital care, including careful fluid and electrolyte management, monitoring kidney function, blood transfusions when necessary and dialysis for severe kidney injury. Treatment of aHUS is different and may involve complement inhibitors such as eculizumab or ravulizumab.

What does HUS feel like?

HUS may initially feel like a severe stomach infection, with diarrhoea, abdominal cramps and vomiting. As kidney injury and anemia develop, a person may become pale, extremely tired, weak, swollen or produce much less urine. Severe cases can cause headache, confusion or seizures.

How can I avoid hemolytic uremic syndrome?

Preventing STEC infection is the most important step for reducing the risk of typical HUS. Cook meat thoroughly, avoid unpasteurised dairy products, practise good hand hygiene, prevent cross-contamination during food preparation and seek medical advice promptly for bloody diarrhoea.

Which bacteria may cause hemolytic uremic syndrome?

The most important bacterial causes are Shiga toxin-producing E. coli, particularly STEC strains, and Shiga toxin-producing Shigella dysenteriae. Streptococcus pneumoniae is another recognised but less common cause.

How is hemolytic uremic syndrome (HUS) treated?

Treatment depends on the type of HUS. Typical STEC-associated HUS is managed mainly with supportive care. Dialysis may be required for severe kidney failure, while blood transfusions can be given when clinically necessary. Atypical HUS may require complement-inhibiting treatment. The underlying infection or trigger is also addressed when appropriate.

The key takeaway

Hemolytic uremic syndrome is uncommon but potentially life-threatening. The combination of recent diarrhoea, particularly bloody diarrhoea, followed by reduced urine, pallor, unusual tiredness, bruising or swelling should raise immediate concern.

The classic HUS triad is hemolytic anemia, low platelets and acute kidney injury. Because kidney damage can develop rapidly, early diagnosis and supportive treatment are crucial.

Most people with typical HUS recover, but recovery does not always mean the end of follow-up. Blood pressure, urine protein and kidney function may need to be monitored after the acute illness to identify any lasting kidney problems early.

Medical disclaimer: This article is intended for general health education and does not replace an examination, diagnosis or treatment plan from a qualified healthcare professional. Suspected HUS requires urgent medical assessment, particularly when reduced urine output, bloody diarrhoea, unusual bruising, severe weakness or altered alertness occurs.

To consult a Nephrologist at Sparsh Diagnostic Centre, call our helpline number 9830117733.

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No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

Medical references

• Mayo Clinic – Hemolytic uremic syndrome
• NCBI Bookshelf – Hemolytic Uremic Syndrome
• Cleveland Clinic – Hemolytic Uremic Syndrome
• CDC – Signs of Hemolytic Uremic Syndrome
• CDC – Treatment of E. coli Infection