Hemolytic uremic syndrome

Alternate Names

HUS; Acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia associated with distorted erythrocytes ('burr cells')

Definition

Hemolytic uremic syndrome, or HUS, is a kidney condition that happens when red blood cells are destroyed and block the kidneys' filtering system.

Red blood cells

Red blood cells contain hemoglobin—an iron-rich protein that gives blood its red color and carries oxygen from the lungs to all parts of the body.

Acute kidney injury

When the kidneys and glomeruli—the tiny units within the kidneys where blood is filtered—become clogged with the damaged red blood cells, they are unable to do their jobs. If the kidneys stop functioning, a child can develop acute kidney injury—the sudden and temporary loss of kidney function. Hemolytic uremic syndrome is the most common cause of acute kidney injury in children.

Cause

Hemolytic uremic syndrome often occurs after a gastrointestinal infections with E. coli bacteria (Escherichia coli 0157:H7). The condition has also been linked to other gastrointestinal infections, including shigella and salmonella, as well as infections outside of the gastrointestinal system. The condition results when the bacteria lodge in the digestive tract and produce toxins that can enter the bloodstream. The toxins travel through the bloodstream and can destroy blood cells, causing acute kidney injury.

Normally, harmless strains, or types, of E. coli are found in the intestines and are an important part of digestion. However, if a child becomes infected with the O157:H7 strain of E. coli, the bacteria will lodge in the digestive tract and produce toxins that can enter the bloodstream. The toxins travel through the bloodstream and can destroy the red blood cells. E.coli O157:H7 can be found in

• undercooked meat, most often ground beef
• unpasteurized, or raw, milk
• unwashed, contaminated raw fruits and vegetables
• contaminated juice
• contaminated swimming pools or lakes

Less common causes, sometimes called atypical hemolytic uremic syndrome, can include

• taking certain medications, such as chemotherapy
• having other viral or bacterial infections
• inheriting a certain type of hemolytic uremic syndrome that runs in families

Risk factors

Children who are more likely to develop hemolytic uremic syndrome include those who

• are younger than age 5 and have been diagnosed with an E. coli O157:H7 infection
• have a weakened immune system
• have a family history of inherited hemolytic uremic syndrome
• Hemolytic uremic syndrome occurs in about two out of every 100,000 children.

In hemolytic uremic syndrome, toxins destroy red blood cells. These misshapen cells may clog the tiny blood vessels in the kidneys.

Signs and symptoms

A child with hemolytic uremic syndrome may develop signs and symptoms similar to those seen with gastroenteritis—an inflammation of the lining of the stomach, small intestine, and large intestine— such as

• vomiting
• bloody diarrhea
• abdominal pain
• fever and chills
• headache

As the infection progresses, the toxins released in the intestine begin to destroy red blood cells. When the red blood cells are destroyed, the child may experience the signs and symptoms of anemia—a condition in which red blood cells are fewer or smaller than normal, which prevents the body's cells from getting enough oxygen.

Signs and symptoms of anemia may include

• fatigue, or feeling tired
• weakness
• fainting
• paleness

As the damaged red blood cells clog the glomeruli, the kidneys may become damaged and make less urine. When damaged, the kidneys work harder to remove wastes and extra fluid from the blood, sometimes leading to acute kidney injury.

Other signs and symptoms of hemolytic uremic syndrome may include bruising and seizures.

When hemolytic uremic syndrome causes acute kidney injury, a child may have the following signs and symptoms:

• edema—swelling, most often in the legs, feet, or ankles and less often in the hands or face
• albuminuria—when a child's urine has high levels of albumin, the main protein in the blood
• decreased urine output
• hypoalbuminemia—when a child's blood has low levels of albumin
• blood in the urine

Thrombotic microangiopathy

Diagnosis

A health care provider diagnoses hemolytic uremic syndrome with

• a medical and family history
• a physical exam
• urine tests
• a blood test
• a stool test
• kidney biopsy

Medical and Family History Taking a medical and family history is one of the first things a health care provider may do to help diagnose hemolytic uremic syndrome.

File:Eculizumab (Soliris).jpg

Eculizumab (Soliris)

Physical Exam A physical exam may help diagnose hemolytic uremic syndrome. During a physical exam, a health care provider most often

• examines a child's body
• taps on specific areas of the child's body

Urine Tests A health care provider may order the following urine tests to help determine if a child has kidney damage from hemolytic uremic syndrome.

Dipstick test for albumin. A dipstick test performed on a urine sample can detect the presence of albumin in the urine, which could mean kidney damage. The child or caretaker collects a urine sample in a special container in a health care provider's office or a commercial facility. For the test, a nurse or technician places a strip of chemically treated paper, called a dipstick, into the child's urine sample. Patches on the dipstick change color when albumin is present in the urine.

Urine albumin-to-creatinine ratio. A health care provider uses this measurement to estimate the amount of albumin passed into the urine over a 24-hour period. The child provides a urine sample during an appointment with the health care provider. Creatinine is a waste product that is filtered in the kidneys and passed in the urine. A high urine albumin-to-creatinine ratio indicates that the kidneys are leaking large amounts of albumin into the urine.

Acute thrombotic microangiopathy - high mag

Blood Test A blood test involves drawing blood at a health care provider's office or a commercial facility and sending the sample to a lab for analysis. A health care provider will test the blood sample to

• estimate how much blood the kidneys filter each minute, called the estimated glomerular filtration rate, or eGFR. The test results help the health care provider determine the amount of kidney damage from hemolytic uremic syndrome.
• check red blood cell and platelet levels.
• check for liver and kidney function.
• assess protein levels in the blood.

Stool Test A stool test is the analysis of a sample of stool. The health care provider will give the child's parent or caretaker a container for catching and storing the stool. The parent or caretaker returns the sample to the health care provider or a commercial facility that will send the sample to a lab for analysis. Stool tests can show the presence of E. coli O157:H7.

Kidney Biopsy Biopsy is a procedure that involves taking a small piece of kidney tissue for examination with a microscope. A health care provider performs the biopsy in an outpatient center or a hospital. The health care provider will give the child light sedation and local anesthetic; however, in some cases, the child will require general anesthesia. A pathologist—a doctor who specializes in diagnosing diseases—examines the tissue in a lab. The pathologist looks for signs of kidney disease and infection. The test can help diagnose hemolytic uremic syndrome.

Treatment

Treatment may involve:

• Dialysis
• Medicines, such as corticosteroids
• Management of fluids and electrolytes
• Transfusions of packed red blood cells and platelets

Prognosis

This is a serious illness in both children and adults, and it can cause death. With proper treatment, more than half of people will recover. The outcome is better in children than adults.

However, children with hemolytic uremic syndrome may have serious and sometimes life-threatening complications, including:

• acute kidney injury
• high blood pressure
• blood-clotting problems that can lead to bleeding
• seizures
• heart problems
• chronic, or long lasting, kidney disease
• stroke
• coma

Some children may sustain significant kidney damage that slowly develops into chronic kidney disease (CKD). Children who develop CKD must receive treatment to replace the work the kidneys do, either through dialysis or kidney transplantation.

Prevention

You can prevent the known cause, E coli, by cooking hamburger and other meats well. You should also avoid contact with unclean water and follow proper hand washing methods.

NIH genetic and rare disease info

• NIH info on Hemolytic uremic syndrome

Hemolytic uremic syndrome is a rare disease.

Hemolytic uremic syndrome Resources
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