Recurrence of FVIII Inhibitor during Surgery in a Patient with Severe Hemophilia A Receiving Emicizumab Prophylaxis.

Emicizumab, a bispecific monoclonal antibody, benefits patients with severe hemophilia A. It alters laboratory assessments of coagulation activity, requiring anti-idiotype monoclonal antibodies for accurate monitoring. A 64-year-old man, receiving emicizumab regularly, was admitted for laminoplasty. We planned to use FVIII replacement during the perioperative period after confirming the disappearance of inhibitors, monitoring coagulation activity with anti-idiotype monoclonal antibodies. Activated partial thromboplastin time was prolonged on postoperative day 2, prompting an immediate switch to eptacog alfa. The patient recovered without bleeding. This case underscores the necessity of anti-idiotype monoclonal antibodies for accurate monitoring.