Selective IgA Deficiency
The most likely diagnosis is selective IgA deficiency, which predisposes patients to anaphylactic transfusion reactions when exposed to IgA-containing blood products.
Clinical Reasoning
This patient's presentation is classic for an anaphylactic transfusion reaction in the setting of selective IgA deficiency:
Key Diagnostic Features
- Anaphylactic reaction during transfusion: Generalized hives (urticaria) and severe hypotension (70/40 mm Hg) occurring during O-negative packed RBC transfusion
- History of recurrent infections: Multiple episodes of pneumonia suggest an underlying immunodeficiency
- Atopic history: Asthma and eczema are commonly associated with selective IgA deficiency
- Response to epinephrine: Appropriate treatment for anaphylaxis was administered
Why Selective IgA Deficiency?
Selective IgA deficiency is the most common primary immunodeficiency (affecting ~1 in 600 people). Patients with this condition:
- Lack IgA in serum and secretions
- May develop anti-IgA antibodies (particularly IgE class)
- Are at risk for severe anaphylactic reactions when exposed to IgA-containing blood products
- Present with recurrent sinopulmonary infections (explaining her multiple pneumonias)
- Frequently have atopic conditions (asthma, eczema)
The anaphylactic reaction occurred because standard packed RBCs contain residual plasma with IgA, triggering an IgE-mediated response in a patient with pre-formed anti-IgA antibodies 1.
Ruling Out Alternative Diagnoses
Blood Group Incompatibility
- Excluded: She received O-negative blood (universal donor for RBCs)
- ABO incompatibility causes acute hemolytic reactions with hemoglobinuria, back pain, and DIC—not isolated urticaria and hypotension 2
Bacterial Contamination
- Unlikely: Would present with high fever, rigors, and septic shock
- Timing doesn't fit—bacterial contamination typically causes more systemic inflammatory response
Hyper-IgM Syndrome
- Less likely: While this causes immunodeficiency, it doesn't explain the specific anaphylactic transfusion reaction pattern
- Patients would have elevated IgM with low IgG and IgA, but anti-IgA antibodies causing anaphylaxis are characteristic of selective IgA deficiency
Clinical Management Implications
For future transfusions in this patient:
- Use washed RBCs or IgA-deficient blood products to prevent recurrence 3
- Document the reaction clearly in medical records
- Consider formal immunology workup to confirm selective IgA deficiency (measure serum IgA levels)
- Avoid plasma-containing products unless absolutely necessary and appropriately prepared
The combination of recurrent infections, atopy, and anaphylactic transfusion reaction with urticaria and hypotension during standard blood product administration makes selective IgA deficiency the most coherent diagnosis.