A Safe and Novel Outpatient Subcutaneous Vitamin B12 Desensitization Protocol in A Patient with Crohn's Disease and Vitamin B12 Allergy: A Case Report.

Introduction: Although rare, some patients may have a vitamin B12 allergy. Crohn's disease commonly leads to significant vitamin B12 deficiency, especially in those patients that have undergone ileal resection. In these difficult cases, vitamin B12 desensitization may be required.

Case Presentation: Here, we report a successful case of a serial outpatient subcutaneous vitamin B12 desensitization protocol in a 35-year-old female with a past medical history of Crohn's disease status post ileal resection, subsequent vitamin B12 deficiency, and allergy to subcutaneous vitamin B12.

Conclusion: This is the first subcutaneous vitamin B12 desensitization protocol reported to have been safely performed in the outpatient setting.