Anemia after bariatric surgery cannot be explained by iron deficiency alone: results of a large cohort study.

BACKGROUND We sought to identify the frequency and mechanisms of anemia after bariatric surgery in a bariatric surgery program at the Medical College of Wisconsin, (Milwaukee, WI). Anemia after bariatric surgery has often been attributed to iron deficiency, although an inflammatory component might be present, making the anemia after surgery mechanistically complex. METHODS The body mass index and hemoglobin (Hb), vitamin B(12), folate, iron, and ferritin levels were extracted from the records of 1125 patients for ≤4 years after Roux-en-Y gastric bypass. Anemia was defined using the World Health Organization criteria. RESULTS The mean body mass index, Hb, and ferritin decreased after surgery. The body mass index decreased from 50.1 kg/m(2) (95% confidence interval [CI] 49.6-50.6) at baseline to 33.0 kg/m(2) (95% CI 32.3-33.6) at 12 months and remained unchanged thereafter. The Hb level decreased from 13.4 g/dL (95% CI 13.3-13.5) to 12.8 (95% CI 12.6-13.1) and ferritin from 87.5 ng/mL (95% CI 75.2-99.7) to 55.4 (95% CI 42.9-68.0) at 24-48 months, and serum iron increased from 68.4 μg/dL (95% CI 66.8-70.0) to 82.8 (95% CI 76.4-88.7); all P values were <.01. Anemia was present in 12% (95% CI 10-14%) of patients at baseline and had increased to 23% (95% CI 16-30%) at 24-48 months. The changes in ferritin, Hb, and the percentage of patients with anemia were most pronounced in premenopausal women. Vitamin B(12) and folate levels were unaffected. CONCLUSION The baseline incidence of anemia was greater than expected and increased significantly after surgery. The percentage of those with anemia and low ferritin was most significant in premenopausal women; however, the overall iron bioavailability improved significantly with pronounced weight loss, suggesting a reduction in inflammation. These findings indicate that anemia after bariatric surgery cannot be explained on the basis of iron availability and suggest that other mechanisms, currently undefined, contribute to the development of anemia in these patients.