A 9-year-old boy with homozygous sickle cell disease, previously stable on hydroxyurea, presents with sudden worsening lethargy and pallor over 3 days. Hb is 3.6 g/dL from a baseline of 8 g/dL. Reticulocyte count is 0.1%. Bilirubin is normal and there is no hemoglobinuria. The most likely causative agent is:

• A G6PD-deficient red cells exposed to an oxidant drug
• B Parvovirus B19 infection ✓
• C Splenic sequestration crisis
• D Delayed hemolytic transfusion reaction

Explanation

Parvovirus A19 infects erythroid progenitors via the P antigen and temporarily halts red cell production, causing pure red cell aplasia. In chronic hemolysis such as sickle cell disease, where red cell survival is already shortened to about 20 days, this produces a severe aplastic crisis with profound reticulocytopenia. Splenic sequestration shows acute splenomegaly and falling platelets, while hemolytic events would show elevated bilirubin, LDH, and reticulocytes rather than a near-zero count.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.