A 63-year-old male patient with diffuse large B-cell lymphoma (DLBCL) received a subcutaneous injection of 20 mg efbemalenograstim alfa 48 hours after chemotherapy with the "zuberitamab+CHOP" regimen to prevent neutropenia. Thirty minutes after administration, the patient suddenly developed symptoms such as dyspnea, pale complexion, cold and clammy limbs, and confusion. Monitoring showed a respiratory rate of 26 breaths per minute and an oxygen saturation of 90%, which was diagnosed as a grade 2 acute allergic reaction. Immediate oxygen therapy, intramuscular injection of 25 mg promethazine, and intravenous injection of 5 mg dexamethasone were given, and the symptoms were relieved. The drug was not used again in subsequent chemotherapy. Grade Ⅲ neutropenia occurred after the third cycle of chemotherapy, and the patient recovered after treatment with short-acting recombinant human granulocyte colony-stimulating factor. After MDT discussion in the fourth cycle, the regimen was adjusted to 6 mg pegylated recombinant human granulocyte colony-stimulating factor, and no adverse reactions were observed during administration. The Naranjo's Assessment Scale scored 7 points, determining a "probable" association between the allergic reaction and efbemalenograstim alfa. This case suggests that acute allergic reaction is a rare adverse reaction of efbemalenograstim alfa. This paper discusses its sensitization mechanism and the adjustment strategy of leukocyte-increasing drugs, providing practical reference for the safe clinical use of the drug.

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