Vitamin B12 and folate deficiencies after allo-HSCT: association with gastrointestinal chronic graft-versus-host disease and anemia

Background. Allo-HSCT recipients, particularly those with gastrointestinal graft-versus-host disease (GI-GvHD), are at increased risk of vitamin B12 and folate deficiencies due to multiple factors, including mucosal injury, reduced intake and drug effects. Data on their prevalence in this population remain limited. Aims. To assess the prevalence of vitamin B12 and folate deficiencies after allo-HSCT and their association with gastrointestinal chronic GvHD and post-transplant anemia. Methods. This retrospective single-center study included allo-HSCT recipients transplanted between 2014 and 2023. Vitamin levels were defined using the lowest recorded values within two years post-transplant. Deficiency thresholds followed NHANES criteria. Results. Among 341 allo-HSCT recipients, decreased vitamin B12 levels (< 300 pg/mL) were observed in 49% of patients (17% <200 pg/mL), and folate deficiency (< 3 ng/mL) in 46%. A subgroup of 68 patients with chronic GvHD was analyzed (median age 45.5 years). Gastrointestinal involvement was present in 42 patients. Median vitamin B12 levels were lower in the GI-GvHD group than in those without GI involvement (258 vs. 442 pg/mL), and deficiency was more frequent (88.6% vs. 11.4%, p < 0.001), with an inverse correlation with GI-GvHD severity ( p < 0.001). Folate levels showed a similar trend without statistical significance. At 12 months post-transplant, hemoglobin concentrations were lower in the GI-GvHD group (12.2 vs. 13.25 g/dL, p = 0.006). Macrocytic anemia predominated in both groups but was not associated with vitamin deficiencies. Conclusions. Vitamin B12 deficiency is common after allo-HSCT recipients and strongly associated with gastrointestinal chronic GvHD. Its lack of association with macrocytic anemia suggests that post-transplant anemia is multifactorial.