What is atypical Haemolytic Uraemic Syndrome (aHUS)?

Atypical Haemolytic Uraemic Syndrome (aHUS) is an extremely rare kidney condition.

Atypical - a rare form of the disease

Haemolytic - breakdown of blood cells

Uraemic - involves the kidneys

Syndrome - patterns of illness that occur together

There are only about 20 new cases of aHUS a year in the UK. As it is so rare, specialist advice is available from the National aHUS Service in Newcastle to help diagnose the condition and advise on treatment.

What are the signs and symptoms of aHUS?

The first sign of aHUS is usually feeling generally unwell, like you have picked up a bug or a virus that doesn’t seem to be getting better.

Symptoms may include:

• feeling or being sick
• diarrhoea
• breathlessness
• headache
• stomach pain
• tiredness
• flu-like symptoms
• blood in the urine (haematuria)
• protein in the urine (proteinuria)

These symptoms may be mild at first but get worse and more noticeable over time. Without treatment aHUS can be life-threatening.

What causes aHUS?

aHUS is caused by a fault in the complement system, which is part of the body’s immune system that helps it to fight infection.

In aHUS a fault in the body’s system of protector proteins causes the complement to attack the body’s cells. This can cause tiny clots to form in small blood vessels in the kidneys. If left untreated, this can lead to kidney damage.

aHUS is caused by either a change in one of the genes that regulate the body’s complement system or by a change in the protector proteins which means they do not work as they should.

In some people aHUS is caused by factor H autoantibodies. These are antibodies which lose this ability to distinguish “self” from “non-self” and stop the protector protein (factor H) from working.

An episode of aHUS can occur at any age, even if the cause of aHUS is due to a genetic change which is present from birth. This is because there is sometimes a ‘trigger’ that starts off the process.

Some of the known triggers for aHUS are:

• gastrointestinal illness – vomiting and/or diarrhoea
• respiratory illness – a cold or flu
• certain medications
• pregnancy – especially in the third trimester and post-delivery

There may be other triggers and, in many cases, no definite trigger for the aHUS episode can be identified.

Does aHUS run in families?

Some cases of aHUS are caused by a genetic change. This means that other family members may also be affected.

If your aHUS is caused by a genetic change, the National aHUS service in Newcastle may offer genetic testing to your family members. However, even if they are found to have the same genetic change, it does not mean that they will definitely develop aHUS. Many people with aHUS genetic changes will never develop the condition.

aHUS that is caused by factor H autoantibodies does not run in families.

Does aHUS affect other parts of the body?

aHUS mainly affects the kidneys but all organs can be affected.

How is aHUS diagnosed?

There is currently no definitive test for aHUS so it is usually diagnosed by blood and urine tests and by ruling out other similar conditions.

Tests may include:

• Full blood count – to examine the haemoglobin (red blood cell) and platelet levels in the blood
• Blood film – to examine your blood cells under a microscope to look for broken or damaged cells
• Lactate dehydrogenase (LDH) measuring – levels of this enzyme can be raised during an episode of aHUS due to the breakdown of red blood cells
• Stool/rectal swab – to exclude ‘typical’ HUS, also known as STEC HUS or diarrhoea positive HUS
• Investigations to rule out other potential conditions

Your local kidney team will also send a blood sample to the National aHUS Service in Newcastle to do some specialist tests, including:

• Genetic testing – to see if you have any of the known genetic faults associated with aHUS
• Factor H autoantibody testing – to see if you have autoantibodies present
• Complement studies – to measure the amount of complement proteins (C3, C4) and protector proteins (Factor H, Factor I, CD46)

In some cases, a kidney biopsy is needed. A needle is used to take a tiny sample (piece) of one of your kidneys to check their function and structure.

It can take several weeks to get the results of these tests. You may be started on treatment before all of the results are back if the National aHUS Service and your local healthcare team think you may have aHUS. This is to stop any further damage to your kidneys. If the tests show that you do not have aHUS, treatment will usually be stopped.

How is aHUS treated?

Without treatment aHUS can lead to kidney failure. However, there are effective treatments available.

Eculizumab

Eculizumab is a medication that blocks the action of complement and stops it from attacking your body’s cells. It is given as an infusion into your veins (intravenously). Each infusion takes around an hour. The infusions take place weekly at first, then every two to three weeks. Once treatment has started, further damage to the kidneys is prevented.

Ravulizumab

If long term treatment is needed, an alternative medication called ravulizumab may be offered. This works in the same way as eculizumab but the infusions only need to be given every four to eight weeks.

Duration of treatment

Recent research has shown that a time limited course of treatment with either eculizumab or ravulizumab is safe. This means that the condition will be treated while it is active, but treatment may be stopped when the aHUS is under control. You will have regular blood tests to monitor your health. Treatment can be re-started if needed.

Dialysis

Some patients may need a short-term course of dialysis to support their kidney function. Dialysis is when a machine is used to clean your blood. This is what kidneys do on their own if they are healthy.

Plasma exchange

In some cases, aHUS patients receive a treatment called plasma exchange. Plasma is the straw-coloured liquid part of the blood that contains minerals, proteins and antibodies. Plasma exchange removes the plasma from your body that contains the faulty proteins and replaces it with fresh plasma containing non-faulty proteins. Plasma exchange is not commonly used in the UK as there are more effective aHUS treatments such as eculizumab.

What are the side effects of treatment?

Eculizumab and ravulizumab block the body’s ability to recognise and destroy the bacteria which causes meningococcal infection. This can increase your risk of developing meningitis (inflammation of the lining around the brain and spinal cord) and/or sepsis (blood poisoning).

Meningitis and sepsis can be life-threatening.

You will receive meningitis vaccinations when you are started on eculizumab or ravulizumab treatment. You will also be prescribed preventative antibiotics which will need to be taken for as long as you remain on eculizumab or ravulizumab.

More information about meningitis is available from the NHS: Meningitis

What is the National aHUS Service?

The National aHUS Service is part of The National Renal Complement Therapeutics Centre (NRCTC). It is based at the Royal Victoria Infirmary in Newcastle-upon-Tyne.

The service opened in 2016 and is commissioned by NHS England and NHS Scotland. They provide advice on the care and management of all patients with suspected or diagnosed aHUS, in partnership with their local kidney healthcare teams.

The team includes:

• Adult and Paediatric Nephrologists with a special interest in kidney complement diseases
• Nurse Consultants and Specialist Nurses
• Service manager, medical secretary and administrative support team
• Specialist consultants and scientists responsible for investigations into blood and genetics

How does the service work?

The National aHUS Service works under a shared care model with local healthcare teams. They share information about patients, including progress on treatment, to make joint decisions about future aHUS management.

If you remain on treatment for aHUS, you will have a consultation with the Newcastle service to be introduced to your consultant and to meet a member of the specialist nursing team.

You can attend consultations remotely using video technology or by telephone. The Newcastle team will provide detailed information on aHUS, treatment options and how your care will be managed.

Where can I find out more information?

• Kidney Care UK is the UK’s leading kidney patient support charity. Our website contains lots of information on kidney conditions, including our rare kidney conditions hub.
• National Renal Complement Therapeutic Centre - aHUS

Publication date: 07/2025

Review date: 07/2028

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