Hemolytic uremic syndrome (HUS)

Date Updated: 07/22/2021

Overview

Hemolytic uremic syndrome (HUS) is a condition that can occur when the small blood vessels in your kidneys become damaged and inflamed. This damage can cause clots to form in the vessels. The clots clog the filtering system in the kidneys and lead to kidney failure, which could be life-threatening.

Anyone can develop HUS, but it is most common in young children. In many cases, HUS is caused by infection with certain strains of Escherichia coli (E. coli) bacteria. The first symptom of this form of HUS is several days of diarrhea, which is often but not always bloody.

HUS may also be caused by other infections, certain medications or conditions such as pregnancy, cancer or autoimmune disease. In some cases, HUS is the result of certain genetic mutations. These forms of HUS usually do not cause diarrhea. .

HUS is a serious condition. But timely and appropriate treatment usually leads to a full recovery for most people, especially young children.

Symptoms

The signs and symptoms of HUS may vary, depending on the cause. Most cases of HUS are caused by infection with certain strains of E. coli bacteria, which first affect the digestive tract. The initial signs and symptoms of this form of HUS may include:

Diarrhea, which is often bloody
Abdominal pain, cramping or bloating
Vomiting
Fever

All forms of HUS — no matter the cause — damage the blood vessels. This damage causes red blood cells to break down (anemia), blood clots to form in the blood vessels and kidney damage. Signs and symptoms of these changes include:

Pale coloring, including loss of pink color in cheeks and inside the lower eyelids
Extreme fatigue
Shortness of breath
Easy bruising or unexplained bruises
Unusual bleeding, such as bleeding from the nose and mouth
Decreased urination or blood in the urine
Swelling (edema) of the legs, feet or ankles, and less often in the face, hands, feet or entire body
Confusion, seizures or stroke
High blood pressure

When to see a doctor

See your doctor immediately if you or your child experiences bloody diarrhea or several days of diarrhea followed by:

Decreased urine output
Swelling
Unexplained bruises
Unusual bleeding
Extreme fatigue

Seek emergency care if you or your child doesn't urinate for 12 hours or more.

Causes

The most common cause of HUS — particularly in children under the age of 5 — is infection with certain strains of E. coli bacteria. E. coli refers to a group of bacteria normally found in the intestines of healthy humans and animals. Most of the hundreds of types of E. coli are normal and harmless. But some strains of E. coli cause diarrhea.

Some of the E.coli strains that cause diarrhea also produce a toxin called Shiga toxin. These strains are called Shiga toxin-producing E. coli, or STEC. When you are infected with a strain of STEC, the Shiga toxin can enter your bloodstream and cause damage to your blood vessels, which may lead to HUS. But most people who are infected with E. coli, even the more dangerous strains, don't develop HUS.

Other causes of HUS can include:

Other infections, such as infection with pneumococcal bacteria, human immunodeficiency virus (HIV) or influenza
The use of certain medications, especially some of the medications used to treat cancer and some of the medications used to suppress the immune system of organ transplant recipients
Rarely, HUS may occur as a complication of pregnancy or health conditions such as autoimmune disease or cancer

An uncommon type of HUS — known as atypical HUS — can be passed down genetically to children. People who have inherited the mutated gene that causes this form of HUS won't necessarily develop the condition. But the mutated gene might be activated after exposure to a trigger, such as an infection, the use of certain medications or a chronic health condition.

Risk factors

The majority of HUS cases are caused by infection with certain strains of E. coli bacteria. Exposure to E. coli can occur when you:

Eat contaminated meat or produce
Swim in pools or lakes contaminated with feces
Have close contact with an infected person, such as within a family or at a child care center.

The risk of developing HUS is highest for:

Children 5 years of age or younger
Adults 65 years of age or older
People who have a weakened immune system
People with certain genetic changes that make them more susceptible to HUS

Complications

HUS can cause life-threatening complications, including:

Kidney failure, which can be sudden (acute) or develop over time (chronic)
High blood pressure
Stroke or seizures
Coma
Clotting problems, which can lead to bleeding
Heart problems
Digestive tract problems, such as problems with the intestines, gallbladder or pancreas

Prevention

Meat or produce contaminated with E. coli won't necessarily look, feel or smell bad. To protect against E. coli infection and other foodborne illnesses:

Avoid unpasteurized milk, juice and cider.
Wash hands well before eating and after using the restroom and changing diapers.
Clean utensils and food surfaces often.
Cook meat to an internal temperature of at least 160 degrees Fahrenheit.
Defrost meat in the microwave or refrigerator.
Keep raw foods separate from ready-to-eat foods. Don't place cooked meat on plates previously contaminated by raw meat.
Store meat below produce in the refrigerator to reduce the risk of liquids such as blood dripping on produce.
Avoid unclean swimming areas. Don't swim if you have diarrhea.

Diagnosis

To confirm a diagnosis of HUS, your doctor is likely to perform a physical exam and recommend lab tests, including:

Blood tests. These tests can determine if your red blood cells are damaged. Blood tests can also reveal a low platelet count, low red blood cell count or a higher than normal level of creatinine, a waste product normally removed by your kidneys.
Urine test. This test can detect abnormal levels of protein, blood and signs of infection in your urine.
Stool sample. This test might detect toxin-producing E. coli and other bacteria that can cause HUS.

If the cause of HUS is not clear, your doctor may also recommend additional tests to help determine the cause.

Treatment

HUS requires treatment in the hospital. Lost fluids and electrolytes must be carefully replaced because the kidneys aren't removing fluids and waste as efficiently as normal.

Transfusions

In the hospital, you may need intravenous (IV) transfusions of red blood cells or platelets.

Red blood cells can help reverse signs and symptoms of anemia — including chills, fatigue, shortness of breath, rapid heart rate, yellow skin and dark urine.
Platelets can help your blood clot more normally if you're bleeding or bruising easily.

Medications

If you have lasting kidney damage from HUS, your doctor might recommend a medication to lower your blood pressure, to prevent or delay further kidney damage.

If you develop complications or have the form of HUS that's caused by a genetic mutation (atypical HUS), your doctor may recommend eculizumab (Soliris) to help prevent additional damage to your blood vessels.

Before taking eculizumab, you will need to receive or have already received a vaccination to prevent meningitis, a potential and serious side effect of the medicine.

Surgery and other procedures

Depending on your symptoms, the cause of your HUS and whether you have any complications, your doctor may recommend other treatments, including:

Kidney dialysis. Sometimes dialysis is needed to filter waste and excess fluid from the blood. Dialysis is usually a temporary treatment until the kidneys begin functioning adequately again. But if you have significant kidney damage, you might need long-term dialysis.
Plasma exchange. Plasma is the fluid part of blood that supports the circulation of blood cells and platelets. Sometimes a machine is used to clear the blood of its own plasma and replace it with fresh or frozen donor plasma.
Kidney transplant. Some people who have severe kidney damage from HUS eventually will need a kidney transplant.

Preparing for an appointment

If you or your child is experiencing symptoms of HUS after several days of diarrhea, call your doctor immediately and be prepared to answer these questions:

Have you noticed blood in the diarrhea?
Have you or your child had a fever, swelling or decreased urine output?
How long have you or your child been experiencing these symptoms?
How long has it been since you or your child urinated?

What you can do in the meantime

If you or your child has an illness that causes vomiting or diarrhea, it's a good idea to try to replace the fluids that have been lost with an oral rehydrating solution, such as CeraLyte, Pedialyte or Oralyte.