A previously normal African-American army recruit was assigned to Southeast Asia and given malarial prophylaxis. He experienced pallor, fatigue, and dark urine. His hemoglobin level decreased from 14.8 to 9 g/dL. The most likely diagnosis is

Correct Answer: D

Rationale: G6PD deficiency (D) causes acute hemolysis with oxidant stress (e.g., antimalarials), common in African-Americans.

Correct Answer: A

Rationale: Elevated transferrin receptor (A) indicates iron deficiency, reflecting increased erythropoiesis demand.

Correct Answer: D

Rationale: Reptilase time (E) isn’t always prolonged with thrombin time (e.g., heparin prolongs thrombin time but not reptilase).

Correct Answer: C

Rationale: Yersinia (C) infection (e.g., enterocolitica) causes mesenteric lymphadenopathy.

Correct Answer: B

Rationale: An IV infusion of factor VIII replaces the missing clotting factor and helps control bleeding.