In a patient who developed a severe anaphylactic reaction after five units of FFP, which testing would help determine the cause given a history of respiratory and gastrointestinal infections?

• A. Complement levels, particularly C3 and C4
• B. Measurement of immunoglobulins
• C. Flow cytometry for T-cell counts
• D. NBT test for phagocytic function

Answer: (B)

A severe anaphylactic reaction to FFP is most consistent with IgA deficiency in which anti-IgA antibodies react to the IgA present in the plasma product. People with this deficiency often have mucosal infections, such as respiratory and gastrointestinal infections, because IgA plays a key role in mucosal immunity. The best way to determine the cause is to measure immunoglobulin levels, focusing on IgA. If IgA is markedly low with otherwise normal IgG and IgM, this supports selective IgA deficiency as the underlying issue, explaining the anaphylactic transfusion reaction. Complement levels, T-cell counts, and phagocyte function testing assess other immune pathways and would not directly pinpoint IgA deficiency as the cause of a transfusion-related anaphylaxis.