Which primary pathophysiologic mechanism corresponds to each of the following patient pres… — USMLE Step 2 CK

Which primary pathophysiologic mechanism corresponds to each of the following patient presentations occurring during or shortly after a blood product transfusion?

A $28$ -year-old female with recurrent sinopulmonary infections develops severe wheezing and profound hypotension within five minutes of initiating a packed red blood cell transfusion.Recipient anti-IgA antibodies binding to donor IgA molecules
A $65$ -year-old male experiences sudden rigors, flank pain, and red-brown urine $45$ minutes after starting a blood transfusion for symptomatic anemia.Preformed recipient antibodies recognizing donor erythrocyte surface antigens
A $72$ -year-old male with a ventricular ejection fraction of $35\%$ develops acute hypoxemia, jugular venous distention, and diffuse pulmonary crackles two hours into a transfusion.Rapid expansion of intravascular volume causing elevated pulmonary hydrostatic pressure
A $34$ -year-old multiparous female develops severe hypoxemia and bilateral pulmonary infiltrates within two hours of receiving fresh frozen plasma, while maintaining a normal central venous pressure.Donor anti-leukocyte antibodies activating recipient neutrophils within pulmonary capillaries
A $40$ -year-old female develops an isolated temperature elevation of $1.5^{\circ}\text{C}$ and mild chills three hours into a transfusion, without any hemodynamic instability or respiratory distress.Release of preformed leukocyte-derived cytokines generated during blood product storage

Answer

IgA deficiency causes anaphylaxis (anti-IgA); ABO incompatibility causes acute hemolysis (anti-donor RBC); volume overload causes TACO (hydrostatic pressure); donor antibodies cause TRALI (neutrophil activation); and storage cytokines cause febrile non-hemolytic reactions.

Each acute transfusion reaction has a distinct pathophysiologic trigger. Anaphylaxis occurs in IgA-deficient individuals who have formed anti-IgA. Acute hemolytic reactions are due to ABO mismatch causing rapid intravascular hemolysis. TACO is simply hydrostatic volume overload in susceptible individuals. TRALI is immune-mediated noncardiogenic pulmonary edema driven by donor anti-leukocyte antibodies. Febrile non-hemolytic reactions are caused by cytokines accumulated during storage.

Step-by-Step Solution

Analyze the timing and clinical signs of the patient with recurrent infections.

Rapid onset hypotension and wheezing indicates an anaphylactic transfusion reaction.

Patients with IgA deficiency form anti-IgA antibodies that react instantly to donor IgA.

Evaluate the patient featuring flank pain and hemoglobinuria.

Symptoms align with acute intravascular hemolysis.

Preformed recipient antibodies (usually anti-ABO) rapidly destroy donor erythrocytes, releasing hemoglobin.

Compare the two patients presenting with respiratory distress post-transfusion.

The patient with low ejection fraction and jugular venous distention has cardiogenic edema (TACO), while the patient with normal central venous pressure has noncardiogenic edema (TRALI).

Distinguishing hydrostatic volume overload (TACO) from immune-mediated neutrophil activation (TRALI) is critical in assessing pulmonary complications.

Assess the patient with an isolated mild fever.

Matches the benign profile of a febrile non-hemolytic transfusion reaction.

Confirms the role of accumulated storage cytokines rather than an acute hemolytic process.

Key Concept

Pathophysiology and clinical differentiation of acute blood transfusion reactions

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