A patient experiences an acute allergic reaction characterized by widespread urticaria, angioedema, and hypotension after receiving a blood transfusion. This reaction involves preformed IgE antibodies bound to mast cells, leading to massive histamine release. This scenario describes which type of hypersensitivity reaction?

The correct answer to the question "A patient experiences an acute allergic reaction characterized by widespread urticaria, angioedema, and hypotension after receiving a blood transfusion. This reaction involves preformed IgE antibodies bound to mast cells, leading to massive histamine release. This scenario describes which type of hypersensitivity reaction?" is Option A: Type I (Anaphylactic).

The other options — B) Type II (Cytotoxic), C) Type III (Immune Complex), D) Type IV (Delayed-type) — are incorrect for this USMLE Exam Prep question. As explained above: Type I hypersensitivity is an immediate reaction mediated by IgE antibodies binding to mast cells and basophils, triggering rapid release of histamine and other inflammatory mediators, leading to sym…