Understanding Hemolytic Uremic Syndrome
This article explains HUS and focuses on the more common, typical form and its symptoms, causes, and treatment.
HUS is easier to understand if you break it down into definitions. “Hemolytic” means the rupture or destruction of red blood cells. “Uremic” means there is a buildup of waste products in the blood that the kidneys usually excrete. These conditions cause a set of symptoms, which medical professionals tend to refer to as a “syndrome.”
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains that the destruction of red blood cells in HUS clogs the glomeruli, which are tiny filters in the kidney. Typically, these filters clean the blood as it flows through the kidneys.
However, clogged glomeruli are unable to remove waste products from the blood. Instead, waste products accumulate in the blood. This condition can be potentially life threatening.
HUS is uncommon. In the United States, there are about 3 cases for every 100,000 people each year. Most cases occur in children younger than 10 years old. In fact, HUS is the most common cause of acute kidney injury in this age group.
There are two types of HUS:
- Atypical HUS: This form is rare. Most cases are genetic or involve an autoimmune reaction that triggers red blood cell destruction. Atypical HUS can become chronic, with repeated episodes throughout a person’s lifetime.
- Typical HUS: More than 90% of HUS cases are the typical form. It is a complication of food poisoning from a specific type of E. coli bacteria that causes gastroenteritis.
The focus of this article is typical HUS.
A Shiga toxin-producing E. coli (STEC) infection is a foodborne illness that causes gastroenteritis. One of the telltale symptoms of a STEC infection is watery diarrhea that becomes bloody. In typical HUS, symptoms usually develop within 1 week of having gastroenteritis.
HUS symptoms may include:
- bloody urine
- areas of bruising
- episodes of bleeding
- decreased urine output
- episodes of fainting
- more paleness than usual
- shortness of breath
- swollen feet, ankles, legs, hands, or face
Get immediate medical care for symptoms of HUS, advises the NIDDK. HUS can lead to potentially life threatening electrolyte imbalances and changes in brain function.
Cases of typical HUS are usually the result of a STEC bacterial infection of the digestive tract.
The Centers for Disease Control and Prevention (CDC) says that in the United States, E. coli STEC O157 is responsible for most outbreaks. Up to 10% of people with this infection will develop HUS. Young children and older adults have the highest risk.
The bacterial Shiga toxin is what causes HUS. The toxin enters the bloodstream after the intestines absorb it. The toxin triggers microclots in the blood. These clots harm red blood cells and use up platelets. This causes low levels of both of these types of blood cells.
The microclots can affect the small vessels in organs, such as the brain and kidneys. Damaged kidneys are unable to function properly to remove waste products from blood. Toxins build up, causing what is known as uremia. This can affect function of other organs, including the heart.
People with an increased chance of developing HUS include:
- children younger than 5 years old
- people with weakened immune systems
- those with a family history of inherited hemolytic uremic syndrome
Learn more about food poisoning causes and risk factors.
To diagnose HUS, doctors will take a medical history and perform an exam, explains the NIDDK. An important part of the history is checking for recent gastroenteritis.
There is no specific test for HUS, but blood tests and urine tests can provide clues. These tests may include:
- complete blood count to check blood cell levels, which may reveal low platelets, red blood cells, and hemoglobin, a protein in red blood cells
- comprehensive metabolic panel to check electrolytes and markers of kidney and liver function, which may show high creatinine levels and electrolyte imbalances
- urinalysis to check for protein and blood in the urine
Doctors may also order stool tests to check for the specific E. coli strain. In some cases, a kidney biopsy may be necessary.
Treating HUS requires care in a hospital. It involves:
- IV in the forms of fluids, electrolytes, and nutrition
- red blood cell and platelet transfusions
- medications to manage blood pressure and other conditions
Dialysis may be necessary to treat acute kidney problems. Dialysis does the work of the kidneys to clean the blood. It gives the kidneys time to heal and recover.
Most people with HUS make a full recovery within a few weeks, according to the CDC. However, some will develop chronic kidney disease afterward. Based on older studies, 5–25% of children with HUS will progress to long-term kidney problems. These problems may require a kidney transplant.
Below are some questions people often ask about HUS.
What is the survival rate of HUS?
Most people survive HUS and recover completely without complications. However, HUS can be fatal. Less than 5% of people who get HUS will die from complications.
Can HUS cause brain damage?
HUS can cause encephalopathy, which is a condition that alters brain function or structure. In HUS, it is the result of uremia and the buildup of waste products in the blood.
How does HUS affect the kidneys?
HUS causes acute kidney injury. In HUS, the kidneys clog with debris from damaged red blood cells. The debris keeps the kidneys from doing their job of cleaning the blood that flows through them. This leads to a buildup of waste products in the blood.
HUS is a condition that affects the blood and kidneys. Most cases are the typical form that develops following a specific type of E. coli infection of the digestive tract. Young children have the highest risk of developing HUS.
There is currently no specific cure for HUS. Rather, clinicians use medications to manage serious symptoms and prevent complications, including organ damage. Kidney dialysis may be necessary. Most people recover without long-term consequences.