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Hemolytic Uremic Syndrome (cont.)

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What is hemolytic uremic syndrome (HUS)?

Hemolytic uremic syndrome (HUS) is a disease of two body systems, the blood stream and the kidney. Hemolysis describes the destruction of red blood cells. In hemolytic uremic syndrome, blood within capillaries, the smallest blood vessels in the body, begins to clot abnormally. When red blood cells pass through the clogged capillaries, they are sheared apart and broken. (hemo=blood +lysis=destruction). The second failed system, kidney failure (uremia), occurs when urea and other waste products build up in the bloodstream because the kidneys cannot filter and dispose of them. (urea=a waste chemical + emia= in the blood).

HUS is also related to another disease caused by a similar normal clotting process within the capillaries called thrombotic thrombocytic purpura (TTP). Within the medical literature, these two conditions are often considered together. HUS is more widely known, however, because it has been discussed in the press because of its relationship to a special type of E. Coli (Escherichia coli) infection associated with food poisoning.

HUS can be classified as typical or atypical. The typical type is associated with gastrointestinal (GI) signs and symptoms including vomiting and diarrhea. Atypical HUS is not associated with GI symptoms.

What causes hemolytic uremic syndrome?

While the cause of HUS has not been established with certainty, researchers believe that an abnormal inflammatory reaction is stimulated in the blood stream causing platelets (the parts of the blood that form clots) to sludge in small blood vessels and form blood clots where they are not supposed to. This uses up the platelets and causes a shortage of them in the rest of the body. This abnormal reaction may be caused by a yet unidentified chemical that is produced in blood plasma (the fluid or non-cellular part of the bloodstream).

The triggering events for HUS are varied and include:

  • Enterohemorrhagic E. Coli is a type of bacteria that causes bloody diarrhea. E. coli is a very common type of bacteria in the body, and it is only the OH157:H7 type that causes the problem. It can be found in undercooked meat and other foods; and is one of the causes of food recalls and restaurant-related food poisoning outbreaks. This accounts for almost 90% of HUS in children. The 2011 outbreak of HUS in Germany was due to a different type of Shigela toxin-producing E. coli called 0104:H4.
  • Pregnancy and the early postpartum (after delivery) time period and the use of birth control pills are the more common associations with HUS.
  • Pneumonia caused by the Streptococcus pneumoniae bacteria is another possible precipitating factor. HUS is rare complication of this common infection. Most often, this pneumonia is treated with antibiotics as an outpatient. However, it is the cause of 40% of atypical HUS.
  • Medications may be also associated with HUS, including some chemotherapy and immunosuppression drugs, birth control pills, ticlopidine (Ticlid, an anti-platelet drug) and quinine (Quinerva, Quinite) an anti-platelet drug.
  • AIDS may be associated with HUS.

Only the diarrheal form of HUS is considered to be typical HUS and is usually a disease of infants and children younger than 3 years of age.

The others are classified as atypical HUS and also include the familial form of the disease in which a gene mutation affects the blood clotting mechanism.

Medically Reviewed by a Doctor on 11/15/2013

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Source: MedicineNet.com
http://www.medicinenet.com/hemolytic_uremic_syndrome/article.htm

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