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What is atypical haemolytic uraemic syndrome?

Atypical haemolytic uraemic syndrome (aHUS) is a very rare kidney condition. It is one type of HUS which arises when blood vessels within the kidney’s tiny filters become blocked by blood clots.

The disease is caused by abnormalities in the complement system. Complement is a part of our immune system that is important in fighting infection. It does this by coating both foreign cells (such as bacteria and viruses) and our own cells (including those of the kidney) with proteins called C3 and C4.

The proteins help to destroy bacteria and viruses by damaging their cell walls. Our cells are normally protected from these complement proteins by other ‘protector proteins’ that help control complement. In aHUS, there are faults in the complement system that means the ‘protector proteins’ don’t work properly. As a result, clots form within the blood vessels within the filters of the kidney causing anaemia, a reduction in platelets (a type of blood cell) and kidney failure.

Causes aHUS?

In most cases aHUS is caused by a genetic fault, which is present at birth. But the disease can start to affect you at any age because it is usually triggered by something such as:

  • pregnancy
  • a viral infection
  • certain medications

If left untreated, aHUS can be life-threatening and will generally result in end-stage kidney failure.

How does aHUS differ from typical HUS?

STEC-HUS (or typical haemolytic uraemic syndrome (HUS) is a similar disease which is generally caused by contracting a bacterial infection, such as those associated with the gastrointestinal bug E. coli O157.

The features of HUS are due to a substance called Shiga toxin that is produced by the E.coli bug, and this form of HUS is now better known as STEC (Shiga-toxin producing E.coli)-HUS. STEC-HUS can also cause sudden kidney failure but usually, you can make a full recovery and have no long-term problems or recurrence of the illness.

aHUS symptoms

Most people with aHUS start by feeling generally unwell and become increasingly tired.

It can make you feel like you’ve picked up a bug and can’t shake it off. Other symptoms include reduced urine production, poor appetite and swelling.

aHUS diagnosis

Urgent blood tests to confirm anaemia, a reduction in platelets and kidney failure can help in diagnosing HUS. However, confirmation of aHUS usually depends on tests to rule out other types of HUS (such as STEC-HUS or other causes of HUS). Complement studies and genetic testing can also help to identify a problem in the complement system that would make aHUS more likely.

aHUS treatment

Until very recently most patients with aHUS faced many years on dialysis. Kidney transplants were rarely an option because the disease would recur in the new kidney.

A new treatment called eculizumab is can now be used to control the complement system.

It can prevent kidney failure in patients with recent onset aHUS and can be given to prevent the recurrence of aHUS in the transplanted kidneys.

Other treatments

Patients with aHUS may also need to have:

  • dialysis for a short period of time (but some people may still need to remain on it in the longer term)
  • plasma exchange – where plasma containing faulty proteins is removed from the body and replaced with fresh plasma containing non-faulty proteins. Plasma is the main component of blood. It is a clear, straw-coloured liquid, which holds platelets, red and white blood cells in suspension. As with dialysis, plasma exchange normally takes a few hours to complete and you will need a line to be inserted into one of your larger blood vessels for it to be carried out.

Resources about aHUS

If you have been diagnosed with aHUS and have any questions or concerns about your illness don’t hesitate to speak to your kidney doctor or nurse or contact The National aHUS Service – a team of aHUS experts based at the Newcastle upon Tyne Hospitals NHS Foundation Trust and Newcastle University.

You can also find further information, advice and helpful tips in our Just diagnosed and How can I help myself? sections.

Reviewed April 2019

Professor David Kavanagh

“Finding the biological causes of aHUS was a true breakthrough."

Professor David Kavanagh

Researcher spotlight

Research by Professor David Kavanagh and his team in Newcastle, supported by Kidney Research UK, has shown that genetic information can help predict which patients diagnosed with atypical haemolytic uraemic syndrome (aHUS) will respond to treatment with a medication called eculizumab.

This research builds on previous breakthroughs in the management of aHUS and offers hope of a more personalised approach.

Meet Ros, who is living with aHUS

Ros Ford shares her story about inheriting a faulty gene that makes people more likely to develop the rare kidney disease aHUS and the impact that research has had on her life.

Our aHUS research

How research can make a difference to people living with kidney disease


Answers for aHUS

In 2016, the aHUSUK charity merged with Kidney Research UK. Volunteers from aHUSUK formed a fundraising and campaigning group called Answers for aHUS.

The group have successfully campaigned to support the approval of eculizumab for use with aHUS patients. aHUS patients in England are able to receive eculizumab when they need it for as long as they need it. This will lead to patients with aHUS having more successful transplants, reducing the risk of the disease attacking their new kidneys.

For more information or support with any Answers for aHUS fundraising please contact 0300 303 1100 or

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