Atypical Hemolytic Uremic Syndrome

Medically Reviewed by Minesh Khatri, MD on September 12, 2023
5 min read

Atypical hemolytic uremic syndrome (aHUS) is a disease that causes blood clots in small blood vessels in your kidneys and other organs. These clots keep blood from getting to your kidneys, which can lead to serious medical problems, including kidney failure. There's no cure, but treatment can help manage the condition.

Besides kidney failure, complications from aHUS can include:

  • Hemolytic anemia (red blood cells dying faster than you can make them)
  • Thrombocytopenia (low blood platelet count)

Atypical hemolytic syndrome is different from "typical" hemolytic uremic syndrome and can cause similar problems. It is classically due to certain bacteria that can cause diarrhea including E. Coli and Shigella.

You can get aHUS at any age. In kids, an equal number of boys and girls get it. Later in life, more women than men tend to get it because pregnancy can be a trigger for the disease.

Atypical hemolytic uremic syndrome is rare. Experts don't know exactly how many people have it, but some studies say it affects only 2 people out of every million in the U.S.

Most aHUS cases happen because of a change called a mutation in a gene. The mutation itself isn't enough to cause the disease. The disease symptoms start after certain things trigger them, such as:

  • Pregnancy
  • Infection
  • Cancer
  • Certain medications
  • Organ transplant
  • Certain chronic diseases, such as systemic sclerosis or malignant hypertension

Up to half of people with aHUS don't have a gene mutation doctors can find. This type of aHUS is called "idiopathic," meaning the cause is unknown. Researchers think these cases of aHUS are due to gene mutations they haven't been able to identify.

Symptoms of aHUS typically come on suddenly after a trigger. These flare-ups can be mild or severe. Mild flare-ups may not affect your kidneys, but severe ones can cause kidney failure.

Some of the symptoms you may have in the early stages of aHUS include:

  • Weakness and a lack of energy
  • General feeling of being sick

The disease is "progressive," which means the symptoms will get worse over time, especially if your doctor isn't able to diagnose it during the early stage.

The main organs affected when you have aHUS are your kidneys. But blocked blood flow can also damage other organs in your body such as your brain, liver, lungs, and heart.

Complications are common and include:

  • Kidney damage or failure
  • High blood pressure
  • Heart disease or heart attack
  • Headaches
  • Double vision
  • Facial paralysis
  • Seizures

Diagnosing aHUS can be tricky if you don't have a family history of the disease. A nephrologist (kidney doctor) or hematologist (blood doctor) will be most likely to know about aHUS. They'll look for these signs:

  • Hemolytic anemia
  • Low count of platelets (blood cells that help with clotting)
  • Kidney problems

You likely will get a complete blood count (CBC) test to measure your platelet and red blood cell levels.

Your doctor may check how well your kidneys are working with a routine test called eGFR (estimated glomerular filtration rate), which is based on the levels of creatinine (a waste product) in your blood. 

Because aHUS can look a lot like a condition called thrombotic thrombocytopenic purpura (TTP), your doctor will also test your blood for a specific protein called ADAMTS13. If your levels are low, you have TTP instead of aHUS.

Genetic testing can also help your doctor figure out if you have aHUS. But a genetic test won't always show aHUS because researchers haven't identified all the genes involved with the disease. 

To be sure you get the most out of a doctor visit, write down your symptoms and a list of questions you want to ask. It's helpful to have a loved one with you to help you understand the information your doctor gives you.

You can ask:

  • What is the best treatment for me?
  • What are the goals of treatment?
  • Will my treatment have any side effects?
  • Should I have a genetic test?
  • Should I see a specialist?
  • Are there any clinical trials I could be a part of?

The FDA has approved two drugs to treat aHUS:

Both drugs are monoclonal antibodies. These are human-made proteins that act like natural antibody proteins in your body. They attach to other proteins called antigens. Once they attach, they tell your immune system to destroy cells with that antigen.

Eculizumab can increase your blood platelet and red blood cell counts. If you take it early enough, it can also reverse any kidney damage you have.

Your doctor will give you eculizumab by injection in their office. You may have side effects from the drug, including:

  • Headache
  • Irritated nose or throat
  • Cold or flu-like symptoms
  • Back pain
  • Constipation
  • Nausea, diarrhea, or stomach pain
  • Feeling dizzy, tired, or weak
  • Trouble sleeping
  • Muscle or joint pain
  • Arm or leg pain
  • Muscle spasms
  • Hair loss

You can also get ravulizumab as an injection. Common side effects include high blood pressure, headache, and cold symptoms. You could also have digestive system problems such as diarrhea, nausea, and vomiting.

Eculizumab and ravulizumab are a type of drug called complement inhibitors. These kinds of drugs may carry a risk of getting meningococcal disease. The CDC suggests people taking them get a meningococcal vaccine. Your doctor may also suggest you take antibiotics to help prevent meningococcal disease.

Besides eculizumab and ravulizumab, you can also treat the symptoms of aHUS with plasma therapy. Plasma is a liquid portion of your blood that takes important nutrients, hormones, and proteins throughout your body.

When you get plasma therapy, you may either have a plasma infusion or plasma exchange.

In a plasma infusion, a doctor puts plasma from a donor into your body. In a plasma exchange, a doctor filters plasma parts out of your blood and replaces them with donor plasma.

If your kidneys don't respond to treatment, you may need kidney dialysis or a kidney transplant.

Some people who have aHUS have one flare-up. Others have regular flare-ups that can be serious. When you're diagnosed, you may need to stay in the hospital for some time.

Although aHUS is a lifelong condition, with early treatment you can manage the effects. Stay in contact with your doctors so they can monitor your health and keep you on track with therapies and symptom management.

It's helpful to talk to family and friends to get the emotional backing you may need as you manage your condition. You can also ask your doctor about how to join a support group, where you'll get to talk to other people with aHUS who understand what you're going through.

There are several organizations you can connect with to find information, the latest research, and others dealing with aHUS and other rare diseases. Often these groups have opportunities to get involved as a patient advocate, which can help doctors develop better treatments.

Resources include:

  • Organizations specifically centered on aHUS, such as aHUS Alliance and the Atypical HUS Foundation
  • Kidney-focused organizations, such as American Association of Kidney Patients, American Kidney Fund, and National Kidney Foundation
  • Rare disease organizations, such as the Genetic and Rare Diseases Information Center and the National Organization for Rare Disorders