What is hemolytic uremic syndrome?
Hemolytic uremic syndrome, or HUS, is a medical condition that affects the smallest blood vessels in different organs causing them to be blocked. This leads to destruction of red blood cells (hemolytic anemia) and reduction in the clotting cells called platelets (thrombocytopenia). Organs most commonly affected include the kidneys (kidney failure) and the brain (confusion, seizures).
HUS was previously grouped with another diagnosis called thrombocytopenic thrombotic purpura (TTP) and referred to as “HUS/TTP” because they had similar symptoms. However, it is now known that they are separate diseases and should not be confused. The term “HUS” is now reserved for the process described below when it is caused by an infection of the GI tract with E coli. Other causes of this presentation are referred to as “atypical” HUS, and make up less than 10% of cases.
Hemolytic uremic syndrome is a common cause of acute kidney injury in children.
Who is most at risk for hemolytic uremic syndrome?
Those who are more likely to develop hemolytic uremic syndrome are:
- Children younger than five years old
- Individuals who eat undercooked meat or unpasteurized milk
- Individuals with direct contact with someone who has diarrhea due to one of the above infections
Symptoms and Causes
What causes hemolytic uremic syndrome?
Hemolytic uremic syndrome affects both children and adults who developed an infection of their digestive system by a specific strain of Escherichia coli (E. coli, O157:H7) that produces a chemical called shiga toxin or less commonly a strain of shigella called Shigella dysenteriae type 1. E. coli. Not all E. coli is toxic; in fact, there are types of E. coli bacteria in the intestines that are good and actually help digestion. E. Coli O157:H7 produces toxins in the intestines that cause diarrhea, travel into the bloodstream, destroy red blood cells, and damage the kidneys.
This toxic strain of E.coli enters the body when a child or adult eats spoiled, undercooked, or poorly processed foods, such as:
- Undercooked meat (usually ground beef)
- Milk or fruit juices that have not been pasteurized, a heating process to kill germs
- Unwashed, contaminated raw fruits and vegetables
Not washing hands well after contact with farm animals and exposure to unclean water in swimming pools or lakes can also be a source of E. coli O157:H7 bacteria.
Diarrhea caused by these bacteria is severe and often bloody.
What are the symptoms of hemolytic uremic syndrome?
Symptoms of E. coli gastroenteritis are:
- Diarrhea (usually bloody)
- Stomach pain
Having diarrhea does not mean you have HUS. There are many causes of bloody diarrhea. But any cause of severe diarrhea (when you cannot stay hydrated or it lasts longer than three days) or any case of bloody diarrhea requires medical attention.
Those people who go on to develop HUS have other symptoms as well. Because the toxins being released in the intestine begin to destroy red blood cells, some people may appear pale and have less energy as the disease progresses. The decrease in red blood cells prevents the body from getting enough oxygen. As the clotting cells called platelets are used up, some people may find that they bruise very easily. Patients may also develop a fever during this process.
If the disease continues to progress and the damaged red blood cells clog the tissue in the kidneys, waste is unable to be filtered and eliminated from the body. This can ultimately lead to acute kidney injury, which has the following signs and symptoms:
- Decreased urine output
- Blood in the urine
- Feeling sick from an increase in the blood toxin levels if this goes on for too long
If the blood vessels in the brain are involved, patients can become confused, sleepy or may even develop seizures.
Diagnosis and Tests
How is hemolytic uremic syndrome diagnosed?
A doctor will ask questions about the patient’s medical and family history and complete a physical exam. The following tests may be ordered:
- Urine testing looking for blood or protein: This is initially performed by a dipstick test on a urine sample.
- Blood tests: Running tests on the patient’s blood will give the doctor details on red blood cell and platelet levels, liver and kidney function.
- Stool test: This test checks a small sample of the patient’s stool to see if E. coli O157:H7 bacteria are present.
- Kidney biopsy: Although this test is not necessary for diagnosis of hemolytic uremic syndrome, it may be ordered by the doctor, if necessary. The patient is given anesthesia so that the doctor can make a small cut in the body in order to take a small piece of the kidney’s tissue and exam it closely under a microscope. In many cases when there is a history of diarrhea and kidney failure, with hemolytic anemia and low platelets, especially if an E. Coli infection is found, a kidney biopsy is not necessary.
Management and Treatment
How is hemolytic uremic syndrome treated?
Treatment of hemolytic uremic syndrome requires a hospital stay. Intravenous (IV) fluids may be given to keep the patient hydrated. Elevated blood pressure that may occur as part of the kidney failure may require medications to bring it down. If the kidney failure is severe enough, dialysis may be needed (usually temporary) to keep the blood clean while the kidneys heal. With proper care, patients with the disease can recover without permanent damage to their health. Antibiotics are not needed to treat diarrhea. The infection will resolve on its own. The use of antibiotics has in some studies been associated with an increased risk of developing HUS.
Children recover more easily than adults with the disease. More than 85% of patients with the most common form of HUS recover complete kidney function. However, even with full recovery, high blood pressure or other kidney problems may affect the patient in the future.
What are the complications of hemolytic uremic syndrome?
Patients with hemolytic uremic syndrome may have serious and sometimes life-threatening complications, including:
- Permanent kidney damage
- High blood pressure
How can hemolytic uremic syndrome be prevented?
Following this list of simple tasks may help prevent hemolytic uremic syndrome due to E. coli O157:H7:
- Avoid unclean swimming areas.
- Avoid unpasteurized milk, juice, and cider.
- Clean kitchen utensils and food surfaces often.
- Cook meat to an internal temperature of at least 160°F/70°C.
- Defrost meat in the microwave or refrigerator.
- Keep children out of pools if they have had diarrhea.
- Separate raw foods from cooked items.
- Wash hands before eating.
- Wash hands after using the restroom and after changing diapers.
- Wash hands after petting farm animals.
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