A 73-year-old, 104 kg female patient was hospitalised for debulking and low anterior colon resection operations. Anaphylactoid symptoms developed when administering erythrocyte suspension and fresh frozen plasma. Through the immediate haematology department consultation, it was found that the patient might possibly have immunoglobulin A deficiency. Immunoglobulin A level was found to be very low in the patient’s blood sample, which was sent intraoperatively to verify the diagnosis. This case report discusses a sudden anaphylactic reaction that occurred as a result of a blood transfusion in a previously undiagnosed immunoglobulin A deficiency.