What is a "syndrome?"
The definition of a syndrome in medicine is a collection of
symptoms (patient complaints), signs (findings on physical
examination), and laboratory or imaging findings that tend to
group together and be associated with a specific disease or
illness.
What is hemolytic uremic syndrome (HUS)?
Hemolytic uremic syndrome (HUS) is a disease of blood clotting
within the capillaries, the smallest blood vessels in the body. As
red blood cells pass through the clogged capillaries, they are
sheared apart and broken. This is called hemolysis and accounts
for the first part of the syndrome's name. The other half of the
syndrome's name refers to kidney failure in which urea and other
waste products build up in the bloodstream because the kidney
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
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.
What are the signs and symptoms of
hemolytic uremic syndrome?
In E. coli-related HUS, gastroenteritis occurs with abdominal
cramping, vomiting and profuse bloody, watery diarrhea. This may
cause significant dehydration, weakness and lethargy, as well as
electrolyte imbalances because of the loss of sodium and potassium
in the vomit and diarrhea. These symptoms tend to resolve before
the onset of HUS.
The anemia and uremia usually present with weakness, lethargy, and
sleepiness. Purpura or small bleeding areas in the skin may be
seen because of low platelet counts.
How is hemolytic uremic syndrome
diagnosed?
The healthcare provider will have a suspicion of the disease based
on the history and physical examination. Abnormal laboratory tests
help confirm the diagnosis. They include:
Hemolytic anemia: the red blood cell count is low and a
peripheral blood smear, in which blood is examined under a
microscope, will show that the red cells have been damaged and
destroyed. This differentiates hemolysis (hemo=blood + lysis=destruction)
from anemia caused by decreased production of blood cells in the
bone marrow.
Thrombocytopenia: a low platelet count
Uremia: Kidney function can be measured by testing the
level of waste products in the blood normally filtered by the
kidney. Creatinine is a breakdown product of a muscle protein
called creatine .When this level rises, it is an indication of
kidney failure or uremia.
Abnormal urine findings: Blood and protein may be found in
the urine when normally they are not present.
Stool cultures: Since E. coli O157:O7 is the most common
cause of HUS, attempts are made to culture the bacteria from stool
samples. The body usually clears the bacteria from the stool
within a week, so a negative test does not exclude the disease. A
positive test helps confirm HUS and will be reported to public
health authorities to try to determine the source of the
infection. Recent public health success stories in the news
include tracking down tainted spinach from a single farm in
California that sickened many around the country.
One of the distinguishing findings between HUS and TTP is a normal
neurologic examination. The brain function is normal in HUS.
What is the treatment for hemolytic
uremic syndrome?
HUS in children tends to be self-limiting, and supportive care is
often all that is needed. This may include intravenous fluids for
rehydration and rebalancing of electrolytes like sodium and
potassium, which can be lost with the diarrhea.
Blood transfusion are only used for the most severe cases of
anemia in which the hemoglobin falls below 6 or 7 g/dL (depending
on age, the normal value is 11-16).
Kidney failure can be managed expectantly (by observation and
supportive care), and dialysis is not often required.
Adults with HUS tend to become more ill and need more aggressive
therapy than children with the condition. In addition to the
supportive care discussed above, plasmapheresis or plasma exchange
may be required. Since it is thought there is an abnormal chemical
in the plasma stimulating the abnormal clot formation, removing
the plasma and replacing it with donor plasma is helpful in
treating adult HUS.
Temporary dialysis may be needed while awaiting recovery of the
kidneys from the illness.
What is the outcome of hemolytic uremic
syndrome?
HUS in children tends to be self-limiting, and full recovery
should be expected.
Adults do less well. Without aggressive therapy like
plasmapheresis and dialysis, up to 40% of those affected may die,
and 80% may have kidney impairment. With treatment, the death rate
falls to 10% or less and kidney impairment to 25%.
Patients with HUS not related to a diarrheal illness have a worse
prognosis than those whose illness is due to an E. coli infection.
In those patients with genetically caused HUS, relapsing illness
is common as are kidney failure requiring dialysis and death.
How can hemolytic uremic syndrome be
prevented?
Most cases of E. coli-related HUS can be prevented by thorough
cooking of hamburger products. The vast majority of cases of HUS
are caused by poor food handling, and proper technique in the
kitchen is the key to prevention.
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