Vitamin B 12 hypersensitivity: a retrospective multicentre study.

BACKGROUND: Vitamin B12 (Vit B12 ) deficiency (VBD) affects about 20% of those above the age of 60 in the United Kingdom and United States. If untreated, it leads to detrimental health outcomes.

OBJECTIVE: To investigate a cohort of patients with Vit B12 hypersensitivity (VB12H) referred to three UK allergy centres and design a pathway for investigation of VB12H.

METHODS: 29 patients seen between 2014 and 2022 underwent SPT (1mg/ml) with cyanocobalamin (CC) and hydroxycobalamin (HC) and IDT (0.1 and 0.01mg/ml). Patients with negative skin tests underwent a Vit B12 drug provocation test (DPT) with either the index or the alternative drug.

RESULTS: 18 of 29 patients (62%) presented with immediate VB12H. Eight experienced anaphylaxis (four to HC, four to CC) and had positive skin tests to the index drug. One patient reacted to oral and seven to injectable Vit B12 . Seven patients sensitised to one form of Vit B12 tolerated DPT with an alternative Vit B12 . One patient with immediate VB12H reacted to polyethylene glycol in oral cobalamin. Eight of 29 patients presented with delayed HSR; four patients tolerated the IM index formulation whilst two patients tolerated the PO formulation. One patient presented with symptoms consistent with SDRIFE. Three patients were referred due to cobalt allergy.

CONCLUSION: Confirmed VB12H is rare. We propose a comprehensive evaluation protocol that includes Vit B12 skin tests and considers PEG allergy in patients presenting with VB12H.