A hospital's blood bank and transfusion medicine service is reviewing recent adverse event… — USMLE Step 2 CK

A hospital's blood bank and transfusion medicine service is reviewing recent adverse events. Match each patient's clinical presentation following a blood product transfusion with the most likely underlying pathophysiologic mechanism.

A $34$ -year-old man develops severe flank pain, hemoglobinuria, and hypotension $15$ minutes into a packed red blood cell transfusion.Preformed recipient IgM antibodies binding to donor erythrocyte antigens, triggering robust complement activation.
A $65$ -year-old woman experiences a temperature increase of $1.5^{\circ}\text{C}$ and rigors $2$ hours after receiving a blood transfusion, without hemodynamic instability.Release of accumulated storage cytokines and recipient antibodies directed against donor human leukocyte antigens.
A $28$ -year-old man with a history of recurrent sinopulmonary infections rapidly develops stridor, severe bronchospasm, and shock seconds after the transfusion begins.Preformed recipient anti-IgA antibodies reacting with trace amounts of IgA in the donor blood product.
A $52$ -year-old man develops severe hypoxemia and bilateral patchy pulmonary infiltrates $4$ hours after a plasma transfusion; echocardiogram shows a normal ejection fraction.Donor anti-leukocyte antibodies activating recipient neutrophils within the pulmonary microvasculature.

Answer

Acute hemolytic reaction matches to complement activation by preformed antibodies; Febrile non-hemolytic matches to storage cytokines and anti-leukocyte antibodies; Anaphylactic reaction matches to anti-IgA antibodies; TRALI matches to donor antibodies activating recipient neutrophils.

Each transfusion reaction has a distinct timeline, clinical presentation, and immunological mechanism. Acute hemolytic reactions present within minutes with signs of intravascular hemolysis (flank pain, dark urine). Febrile non-hemolytic reactions are milder, presenting with isolated fever hours later due to storage cytokines. Anaphylactic reactions occur in seconds with severe respiratory collapse, classic in IgA-deficient patients exposed to donor IgA. TRALI causes acute hypoxemic respiratory failure due to immune-mediated pulmonary edema without fluid overload, triggered by donor antibodies.

Step-by-Step Solution

Analyze the onset time of the transfusion reaction.

Seconds implies anaphylaxis; minutes implies acute hemolysis; hours implies febrile non-hemolytic or TRALI.

The timeline is highly specific to the underlying immune mechanism.

Evaluate specific organ system involvement and vital signs.

Flank pain and dark urine indicate hemolysis. Stridor and wheezing indicate anaphylaxis. Hypoxemia with clear heart function indicates TRALI. Isolated fever indicates febrile non-hemolytic.

Differentiating these reactions requires linking the clinical syndrome directly to its pathophysiology.

Match the clinical syndrome to the precise immunological trigger.

Each vignette perfectly aligns with a single mechanism from the available choices.

Completes the matching requirement of the question by mapping clinical clues to molecular mechanisms.

Key Concept

Transfusion Reaction Pathophysiology and Clinical Recognition

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