Atypical Hemolytic Uremic Syndrome

Overview

Atypical hemolytic uremic syndrome, often called aHUS, is a very rare but serious condition in which tiny blood vessels throughout the body become damaged. This damage causes blood clots to form, which can block the vessels and lead to low levels of platelets (cells that help blood clot), the destruction of red blood cells (anemia), and injury to the kidneys and other organs. It happens because part of the immune system, called the complement system, becomes overactive and attacks the body's own cells instead of protecting it.

No, aHUS is extremely rare. It is estimated to affect about 2 out of every 1 million people worldwide.

aHUS can affect anyone at any age, but it most often appears in children. It affects males and females about equally. Some people inherit the condition from their parents, while others have no family history.

Symptoms

Common symptoms

• Feeling very tired or weak (fatigue)
• Swelling in the hands, legs, feet, or face
• Decreased urination or dark-colored urine
• Easy bruising or unusual bleeding
• Pale skin because of anemia
• High blood pressure

Symptoms in children

• Fever and irritability
• Pale skin or a yellowish tint to the eyes
• Decreased urination (fewer wet diapers)
• Unexplained bruising or tiny red spots on the skin
• Vomiting or diarrhea

Symptoms in older adults

• Confusion or trouble thinking clearly
• Chest pain or shortness of breath
• Severe swelling in the legs or abdomen
• Blood in the urine
• Difficulty urinating or very little urine

Causes

Main causes

• Overactive complement system, which is a part of the immune system
• Changes (mutations) in genes that control the complement system
• Antibodies that attack the complement system (autoantibodies)
• In some cases, the exact cause is unknown

Risk factors

• Having a family member with aHUS or a related genetic mutation
• Infections, certain illnesses, pregnancy, or certain medicines can trigger it in people who are already at risk
• Having had a kidney transplant or other organ transplant

When to see a doctor

See a doctor urgently if:

• If you notice a sudden drop in urination or dark urine
• If you develop unusual bruising, bleeding, or a severe headache
• If you have chest pain or difficulty breathing
• If you or your child seems unusually confused, sleepy, or disoriented

Book a routine appointment if:

• If you have a family history of aHUS and are thinking about getting tested or having children
• If you have been diagnosed with aHUS and need regular follow-up

Diagnosis

Doctors diagnose aHUS by reviewing your symptoms, taking your medical history, and performing blood and urine tests. The process often happens in a hospital because the condition can quickly become severe. A specialist, such as a kidney doctor or blood specialist, will guide the diagnosis.

Tests that may be done

• Complete blood count to check your red blood cell and platelet levels
• Kidney function test to see how well your kidneys are working
• Urine test for blood or protein
• ADAMTS13 test to rule out a related condition
• Complement system tests to look for overactivity
• Genetic testing to find gene changes linked to aHUS

What to expect at your appointment

You should expect a thorough workup that includes several blood draws and possibly a urine collection. It may take a few weeks for all results to return, especially genetic tests. The care team will likely include kidney and blood specialists, and you may need to stay in the hospital for initial management.

Treatment

Treatment for aHUS focuses on quickly stopping the damage to blood vessels, controlling the immune system, and protecting your kidneys and other organs. The condition is often treated in a hospital, especially during a first episode. The goal is to get the disease under control and prevent relapse.

Self-care at home

• Take all prescribed medicines exactly as directed – never stop or change them without talking to your doctor.
• keep all follow-up appointments and recommended blood tests.
• Watch for signs of relapse, such as fatigue, swelling, or dark urine, and report them immediately.
• Stay hydrated, but follow your doctor's fluid and diet recommendations.
• Avoid known triggers, like infections, and practice good handwashing.

Medical treatments

Doctors may prescribe medicines that block parts of the complement system to stop the small blood vessel damage. This type of treatment is called complement inhibition and is given through an IV or as a shot. In some cases, plasma exchange (also called plasmapheresis) is used to remove overactive complement proteins from the blood. Blood transfusions may help with severe anemia, but this is generally avoided unless necessary. Treatment plans are personalized, and your care team will decide what is best for you.

When is surgery considered?

Surgery is not a primary treatment for aHUS. However, if kidney damage progresses to kidney failure, you may need dialysis (a machine to clean your blood) or a kidney transplant. A transplant is considered only after the disease is well controlled with medication.

Living with this condition

Living with aHUS includes regular monitoring, taking medication as prescribed (often for life), and being aware of how your body feels. Many people learn to manage their energy levels and plan ahead for medical appointments. Your care team will help you develop a routine that works for you.

Lifestyle tips

• Get enough rest and pace yourself.
• Keep your vaccinations up to date to prevent infections that could trigger a flare.
• Carry a medical alert card or note that says you have aHUS, especially if you take a complement inhibitor.
• Tell all healthcare professionals, including dentists, about your condition.

Diet and exercise

A kidney-friendly diet is often recommended, which may mean limiting salt, potassium, and phosphorus. Your doctor or dietitian can give you specific advice. Gentle exercise, such as walking or cycling, is usually fine, but always check with your medical team first – especially if you have high blood pressure or are recovering from a flare.

Mental health and emotional wellbeing

Living with a rare, long-term condition can be stressful and can cause anxiety or depression. It is completely normal to feel worried, overwhelmed, or frustrated. Talk to your doctor about mental health support, and consider reaching out to a counselor or support group.

Prevention

aHUS itself cannot be prevented because it is usually caused by an overactive immune system that may be genetic or related to antibodies. However, early recognition and prompt treatment can help prevent serious damage. In people who know they carry the condition, staying up to date with vaccinations and treating infections quickly can reduce the risk of a flare.

Vaccines

Keeping all recommended vaccinations current, especially for influenza and other infections, is important because infections are common triggers for aHUS attacks. Discuss a vaccine schedule with your doctor.

Screening programmes

If you have a family member with aHUS and a genetic cause has been found, genetic testing and counselling can help screen other family members. If you plan to have children, a genetic counsellor can explain your options.

Complications

If left untreated

• Permanent kidney damage leading to kidney failure
• High blood pressure that is difficult to control
• Damage to other organs such as the heart, brain, or eyes
• Stroke or heart attack
• In severe cases, death

Long-term outlook

With early diagnosis and modern treatments, the outlook for aHUS has dramatically improved. Many people regain good kidney function and are able to live full, active lives. The disease can be unpredictable, and treatment is often lifelong, but ongoing support helps keep it under control. Your medical team will work with you to achieve the best possible outcome.

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