HUS is a rare disorder in which many small blood clots (thrombi) form suddenly throughout the body. Hemolytic means that red blood cells break down, and uremic means that kidney injury causes urea (a waste product) to accumulate in the blood. HUS is related to thrombotic thrombocytopenic purpura (TTP), but it occurs more often in children and more often causes kidney failure, whereas TTP is more common among adults.
The small blood clots that form in HUS block small blood vessels throughout the body, particularly those in the brain, heart, and kidneys. The blood vessel blockage damages organs and can break apart red blood cells that pass through partially blocked vessels. The blood clots also mean that an abnormally high number of platelets are being used up, which leads to a sharp decrease in the number of platelets in the bloodstream.
Platelets are cells that are made in the bone marrow and circulate in the bloodstream and help blood clot. Platelets are sometimes called thrombocytes. Having too few platelets is termed thrombocytopenia.
Hemolytic-uremic syndrome usually occurs following an intestinal infection that results from ingestion of food contaminated with Escherichia coli O157:H7 or other toxin-producing bacteria.
In hemolytic-uremic syndrome (HUS), symptoms develop suddenly.
Symptoms in HUS are quite distinct from symptoms of most other forms of thrombocytopenia.
In HUS, children usually first have vomiting and diarrhea. The diarrhea is often bloody. The main symptoms of complications of HUS are related to blood clots that develop in the kidneys, causing damage that is usually severe and often progresses to kidney failure, requiring dialysis. HUS does not often cause brain symptoms.
Doctors suspect hemolytic-uremic syndrome (HUS) when they find a low platelet count in children who have been ill or, less commonly, in those who have taken certain drugs.
Although there are no blood tests that specifically diagnose HUS, doctors do a number of blood tests that, together with people's symptoms, help make the diagnosis. These blood tests often include a complete blood count, tests demonstrating that red blood cells are being destroyed such as examination of a sample of blood under a microscope (blood smear), and tests to determine how well the kidneys are working.
About half of children with hemolytic-uremic syndrome temporarily require kidney dialysis. Most often, the kidneys recover, but some children have permanent kidney damage. Eculizumab is a drug that suppresses complement, a component of the immune system. It reduces the rate of kidney damage, and in some people, it may rapidly restore kidney function. People who take eculizumab are at higher risk than normal for meningococcal meningitis, so they should receive the meningococcal vaccine to prevent meningococcal infections.