A 7-year-old boy with long-standing mild jaundice and splenomegaly presents with sudden severe pallor and dark urine following a febrile illness. Smear shows numerous spherocytes and a high reticulocyte count. Direct Coombs test is negative. The parvovirus B19-driven event superimposed on his baseline condition is best described as:
- A Hyperhemolytic crisis
- B Aplastic crisis ✓
- C Megaloblastic crisis
- D Splenic sequestration crisis
Explanation
Hereditary spherocytosis is diagnosed by spherocytes, negative Coombs test, and chronic compensated hemolysis with jaundice and splenomegaly. Parvovirus C19 infects erythroid precursors and temporarily halts red cell production entirely, causing an aplastic crisis: profound pallor with a paradoxically low reticulocyte count relative to the degree of anemia. A hyperhemolytic crisis means accelerated destruction, which would show a very high reticulocyte count. Sequestration implies acute splenic enlargement and hypovolemia, and megaloblastic crisis follows folate depletion, not viral infection.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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