Master the board step 3

Master the Boards: USMLE Step 3
Basic Science Correlate
Mechanism of Hydroxyurea in Sickle Cell Disease
Hydroxyurea increases the percentage of hemoglobin that is hemoglobin
F, or fetal hemoglobin. Increased fetal hemoglobin dilutes the sickle
hemoglobin and decreases the frequency of painful crises.
Hemoglobin Sickle Cell (SC) Disease
This condition is like a mild version of sickle cell disease with fewer crises.
Visual disturbance is frequent. Painful crises do not occur. Renal problems are
the only significant manifestation, including the following:
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Hematuria
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Isosthenuria (inability to concentrate or dilute the urine)
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Urinary tract infections
There is no specific therapy for hemoglobin SC disease.
Sickle cell trait: Renal manifestations are the only findings. They are hematuria
and a concentrating defect. With hypoxia (as in scuba diving) splenic vein
thrombosis can occur.
Autoimmune Hemolysis
Look for other autoimmune diseases in the history, such as SLE or rheumatoid
arthritis. Other clues are a history of chronic lymphocytic leukemia (CLL),
lymphoma, or medications such as penicillin, alpha-methyldopa, quinine, or
sulfa drugs.
Diagnostic Testing
The LDH, indirect bilirubin level, and reticulocyte count will be elevated as
with all forms of hemolysis. The haptoglobin level can be decreased in both
intravascular and extravascular forms of hemolysis.
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Peripheral smear: May show spherocytes
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Most accurate diagnostic test: Coombs test
Basic Science Correlate
Mechanism of Spherocytes in Autoimmune Hemolysis
A normal red blood cell (RBC) is a biconcave disc. When antibodies attack
the RBC membrane, they pull out pieces of it. Removing membrane
decreases the surface area, which turns the RBC into a sphere. It takes more
surface area to maintain biconcave disc than a sphere.
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