Hematology
in hemoglobin A2 and hemoglobin F (beta thalassemia only); target cells, nucleated red blood
cells, and diffuse basophilia on peripheral smears; skull radiogaph with "crew-cut" appearance;
extramedullary hematopoiesis (see figure); splenomegaly; and positive family history. Tha-
lassemia is more common in blacks, Mediterraneans, and Asians.
Extramedullary hematopoiesis. A coronal MRI image of
the thorax in a patient with moderately severe (3-tha-
lassemia reveals multiple round masses in the center and
periphery of the thorax, reflecting foci of extramedullary
hematopoiesis arising from the paravertebral region and
ribs, respectively. (From Hoffbrand AV, Pettit JE: Color
Atlas of Clinical Hematology, 3rd ed. St. Louis, Mosby,
2000, p 95, with permission.)
21. What diagnostic test confirms a diagnosis of thalassemia? How is it treated?
Diagnosis is made by hemoglobin electrophoresis. There are four gene loci for the alpha
chain of hemoglobin but only two for the beta chain. Patients with alpha thalassemia are symp-
tomatic at birth or die in utero (fetal hydrops), whereas patients with beta thalassemia are not
symptomatic until 6 months of age.
No treatment is required for minor thalassemia. Patients are often asymptomatic because
they are used to living with a lower level of hemoglobin. Thalassemia major is more dramatic
and severe. Treat with transfusions, as needed, and iron chelation therapy to prevent secondary
hemochromatosis.
22. What two clues on the Step 2 exam often point to a diagnosis of sickle cell disease?
Peripheral smear and race. Eight percent of African Americans are heterozygous for sickle
cell trait. Know what sickled red blood cells look like. Patients usually have a high percentage of
reticulocytes (8-20%).
23. What are the clinical manifestations and complications of sickle cell disease?
• Aplastic crises (due to parvovirus B19 infection)
• Bone pain (due to infarcts; the classic example is avascular necrosis of the femoral head)
• Dactylitis (also known as hand-foot syndrome, seen in children)
• Renal papillary necrosis
• Splenic sequestration crisis
• Autosplenectomy (increased infections with encapsulated bugs such as Pneumococcus,
Haemophilus, and Neisseria species)
• Acute chest syndrome (mimics pneumonia)
• Pigment cholelithiasis
• Priapism
• Stroke
24. How is sickle cell disease diagnosed and treated?
Diagnosis is made by hemoglobin electrophoresis. Screening is done at birth, but symptoms
usually do not appear until around 6 months of age because of the lack of adult hemoglobin pro-
