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Hemolysis of red blood cells (RBCs) within the circulation or
in the extravascular spaces of the spleen and liver can produce
a spectrum of disease, from mild, asymptomatic illness to severe
hemodynamic compromise leading to critical ED encounters. Acquired
hemolytic anemia consists of hemolysis not due to congenital or
inherited disorders of hemoglobin synthesis or of the RBC membrane.
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Presenting symptoms and signs of hemolytic anemia include those
common to anemia in general: weakness or fatigue; dizziness; shortness
of breath with dyspnea on exertion; tachycardia, particularly at
rest; palpitations; chest pain; new or accentuated cardiac murmur;
and pallor. RBC destruction generates free hemoglobin that is then
broken down into bilirubin. When bilirubin production exceeds the
liver’s ability to conjugate it for biliary and fecal excretion,
jaundice, abdominal pain (particularly from gallstones), and darkened
urine may develop. Splenic enlargement may promote the storage and
extravascular breakdown of RBCs.
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The laboratory findings characteristic of acquired hemolytic
anemia are those that demonstrate blood loss and hemolysis of RBCs,
hemoglobin breakdown, and compensatory RBC production (Table
232-1). The complete blood count (CBC) serves
as the diagnostic cornerstone, providing the anemic level hemoglobin
and hematocrit and the increased reticulocyte count indicative of
the bone marrow’s effort to replace lost RBCs. Findings
on peripheral blood smear demonstrate the abnormal RBC morphology
needed to verify the presence of hemolysis: schistocytes generated
by intravascular shearing of RBCs and spherocytes produced by extravascular
phagocytosis of RBCs within the liver and spleen.
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Intravascular hemolysis of RBCs releases hemoglobin
into the bloodstream that then binds to haptoglobin and other serum
proteins. The hemoglobin-haptoglobin complex travels to the liver
for processing, thus decreasing the amount of free haptoglobin in
the serum—an important laboratory finding when corroborating
the existence of intravascular hemolysis. Breakdown of RBCs releases
lactate dehydrogenase and potassium, leading to elevation of both
in serum. With excessive hemoglobin breakdown comes increased bilirubin
production that cannot be conjugated by the liver for biliary and
fecal excretion. Laboratory findings associated with excess bilirubin
production include elevated total bilirubin; elevated indirect or
unconjugated bilirubin; and increased urinary urobilinogen, a by-product
of bilirubin breakdown formed by the intestine and passed into the
urine. Excess free hemoglobin ...