A 68‑year‑old man with hypertension and myelodysplastic syndrome receiving packed red blood cells develops generalized itching, urticarial hives, low‑grade fever, and stable vitals without hypotension or respiratory distress; what is the most likely diagnosis (anaphylactic transfusion reaction, allergic transfusion reaction, or febrile non‑hemolytic transfusion reaction)?

Allergic Transfusion Reaction

This patient has an allergic transfusion reaction, characterized by isolated urticaria and pruritus with stable vital signs and only minimal temperature elevation (37.9°C), without hypotension or respiratory compromise. 1, 2

Diagnostic Reasoning

Why This Is an Allergic Reaction

• Urticaria (hives) and generalized itching are the hallmark features of allergic transfusion reactions, occurring in approximately 1 in 4,124 blood components transfused. 3
• The patient's vital signs remain stable—pulse 76/min and blood pressure 126/84—ruling out anaphylaxis, which requires hypotension (systolic <90 mmHg or ≥30 mmHg drop from baseline) or respiratory compromise. 1, 2
• The temperature of 37.9°C represents only minimal elevation and does not meet criteria for febrile non-hemolytic transfusion reaction, which typically presents with more prominent fever as the primary manifestation. 2

Why This Is NOT Anaphylaxis

• Anaphylactic reactions are defined by hypotension, bronchospasm, severe respiratory distress, or cardiovascular collapse—none of which are present in this case. 1, 4
• This patient's blood pressure (126/84) and pulse (76/min) are completely normal, excluding the cardiovascular dysfunction required for anaphylaxis diagnosis. 1, 2
• Anaphylaxis occurs in only approximately 1 in 30,281 transfusions and represents severe allergic reactions accounting for 7.7% of all allergic transfusion reactions. 3
• Bradycardia can occur in anaphylaxis, but this patient has a normal heart rate of 76/min, not bradycardia. 2

Why This Is NOT Febrile Non-Hemolytic Transfusion Reaction

• Febrile non-hemolytic transfusion reactions present primarily with fever (often >38°C) as the dominant clinical feature, with an incidence of approximately 1.1% when prestorage leukoreduction is used. 2
• This patient's primary symptoms are dermatologic (hives and itching), not fever—the 37.9°C temperature is minimal and likely represents a mild component of the allergic response rather than a true febrile reaction. 1, 2
• The timing (45 minutes into transfusion) and predominance of cutaneous manifestations clearly point to allergic rather than febrile etiology. 3

Immediate Management Already Initiated

• The nurse correctly stopped the transfusion immediately, which is the single most critical intervention that can prevent progression to severe morbidity. 1, 2
• Maintain IV access with normal saline for medication administration. 2

Next Steps in Management

• Administer antihistamines for symptomatic treatment—second-generation antihistamines like cetirizine 10 mg IV/oral or loratadine 10 mg orally are preferred over first-generation antihistamines like diphenhydramine, which can cause sedation. 1
• Monitor vital signs every 5-15 minutes, including heart rate, blood pressure, temperature, respiratory rate, and oxygen saturation, to detect any progression. 2
• Watch for red flags that would indicate progression to anaphylaxis: development of hypotension, respiratory distress (dyspnea, wheezing, oxygen saturation <92%), or multi-system involvement. 1, 2

Critical Pitfall to Avoid

• Do not assume this mild reaction cannot progress—approximately 26% of allergic transfusion reactions do not initially present with skin manifestations, and reactions can evolve. 3
• If hypotension or respiratory compromise develops, immediately administer epinephrine 0.3-0.5 mg IM into the anterolateral thigh. 1, 4

Prevention of Future Reactions

• Consider antihistamine premedication (cetirizine 10 mg or loratadine 10 mg) for future transfusions, given this documented allergic reaction. 1
• Document this reaction thoroughly in the patient's medical record to ensure appropriate premedication for subsequent transfusions. 2