Supplementary Material for: Beyond Iron Deficiency: Unveiling the Prevalence of Folate and Vitamin B12 Deficiencies in Major Surgical Patients

Introduction: Preoperative anaemia is associated with increased morbidity and mortality in surgical patients. While iron deficiency is a well-recognized cause, the contribution of other nutritional deficiencies, such as folate and vitamin B12, remains underexplored. Therefore, this study aimed to assess the prevalence and role of folate and vitamin B12 deficiencies in preoperative anaemia among patients undergoing major surgery.
Methods: This retrospective observational study included 410 patients aged ≥18 years who underwent major surgery and were evaluated at a preoperative anaemia clinic in a large tertiary hospital between June 2016 and June 2023. Key outcome measures included the prevalence of iron, folate, and vitamin B12 deficiencies and their associations with preoperative anaemia.
Results: Anaemia was observed in 41.5% (95% CI 36.8 to 46.3), iron deficiency in 51.5% (46.6 to 56.3), folate deficiency in 18.0% (95% CI 14.6 to 22.1) and vitamin B12 deficiency in 3.2% (95% CI 1.9 to 5.4). Anaemic patients exhibited higher rates of iron (61.8%, 95% CI 54.3 to 68.7 vs. 44.2%, 95% CI 38.0 to 50.5) and folate deficiencies (27.1%, 95% CI 20.9 to 34.2 vs. 11.7%, 95% CI 8.2 to 16.3, P <0.001) compared to non-anaemic patients. Combined deficiencies, primarily iron and folate, were more frequent in anaemic patients (17.7%, 95% CI 12.7 to 24.1 vs. 7.5%, 95% CI 4.8 to 11.5, P =0.003). Substantial heterogeneity in deficiency patterns was observed across surgical subgroups, with overall prevalences ranging from 20% to 59% for iron, and from 11% to 31% for folate.
Iron (OR 3.27, 95% CI 2.03 to 5.27, P <0.001) and folate (OR 2.6, 95% CI 1.45 to 4.59, P =0.001) deficiencies were independently associated with anaemia and together accounted for approximately one-third of preoperative anaemia cases.
Conclusion: Iron deficiency remains the predominant contributor to preoperative anaemia, with folate deficiency playing a significant yet underrecognized role. The high occurrence of combined deficiencies and substantial heterogeneity across surgical populations support the need for population-specific diagnostic and supplementation strategies.