Preoperative Iron Status and the Risk of Severe Postoperative Anemia After Metabolic and Bariatric Surgery

Iron deficiency (ID) is the most common nutritional deficiency following metabolic and bariatric surgery. Preoperative anemia and/or low serum levels of ferritin, which are common among candidates for metabolic and bariatric surgery (MBS), are associated with increased risk of developing severe postoperative ID. This study investigates iron status among candidates for MBS and its relationship to the development of severe postoperative anemia. From an established bariatric surgery registry, surgery candidates with iron assessment as well as longitudinal anemia follow-up were identified. The relationship between ferritin levels < 30 ng/mL stratified by levels of transferrin saturation < 20% and < 15% was analyzed to identify risk factors associated with the onset of severe postoperative anemia (hemoglobin level < 8 g/dL). Four thousand seven hundred and nine patients were studied. 14.6% had ferritin concentrations < 30 ng/mL and another 20% 30-99 ng/dL coupled with transferrin saturations (TSATs) < 20% to indicate absolute ID and functional ID. The overall prevalence of ID was 35%. The overall risk of severe postoperative anemia was 10.5% at 5 years and 19.8% at 10 years. Ferritin levels of < 30 ng/mL and TSAT < 20% were each associated with greater risk of developing severe anemia (p < 0.0001). Patients with ferritins < 30 ng/mL and TSATs < 15% had the most severe ID with the greatest risk of developing earlier and more severe anemia which was confirmed after adjusted analysis (p < 0.0001). A preoperative ferritin level < 30 ng/mL with TSAT < 15% is an excellent predictor for severe postoperative anemia.