A comparison of intravenous iron formulations for treating iron deficiency anemia after bariatric surgery Free

Background:

Iron deficiency (ID) is common following bariatric procedures and frequently leads to anemia. While oral iron is the first-line therapy, the American Gastroenterological Association recommends intravenous (IV) iron—particularly for patients undergoing surgeries like Roux-en-Y or sleeve gastrectomy where duodenal absorption is disrupted and iron-deficiency anemia exists without overt gastrointestinal blood loss. Newer IV iron formulations that can correct deficits in one or two infusions (ferric carboxymaltose, ferric derisomaltose, and ferumoxytol) are favored over multiple-infusion agents like iron sucrose. Although IV iron may be more effective, potential side effects—such as post-infusion hypophosphatemia—must be carefully monitored post-bariatric surgery, as secondary hyperparathyroidism from vitamin D deficiency and calcium malabsorption may exacerbate this complication.

Methods:

We performed a retrospective, single-center study of adult patients treated with IV iron for iron-deficiency anemia (IDA) after bariatric surgery from January 2021 to March 2025. Exclusion criteria included chronic kidney disease, pregnancy, and autoimmune disorders. Laboratory data (hemoglobin, ferritin, transferrin saturation, and phosphate) were collected at baseline (Month 0, defined as the time of IV iron initiation) and at 6, 12, 18, and 24 months post-treatment. ID was defined as ferritin < 15 ng/mL; anemia as Hb < 11.7 g/dL; and IDA required both criteria. Hypophosphatemia was defined as phosphate < 2.5 mg/dL. At Months 0 and 12, additional labs were recorded—including RBC count, MCHC, MCV, and calcium. History of vitamin D deficiency, as documented in the clinical record, was also recorded. Between-group comparisons for continuous variables were performed using the Mann-Whitney U test. Categorical variables were compared using Fisher's Exact test.

Results:

Fifty women were included—36 treated with iron sucrose and 14 with newer formulations (ferric carboxymaltose, n = 7; ferric derisomaltose, n = 3; ferumoxytol, n = 4). The median age at surgery and at treatment with IV iron was 37.5 and 46 years, respectively. The cohort was 100% female, predominantly Black (68%), with 98% having failed oral iron before IV therapy. Procedures included Roux-en-Y gastric bypass (62%) and sleeve gastrectomy (38%). Vitamin D deficiency and hypophosphatemia were present in 54% and 4%, respectively. Median follow-up declined over time due to attrition.

Both cohorts showed reductions in the prevalence of iron deficiency, anemia, and IDA over follow-up, with numerically lower rates in the non–iron sucrose group at most time points. Median hemoglobin levels were consistently higher at all time points in the newer-formulation group, though without reaching statistical significance overall. In exploratory subgroup analysis, ferric carboxymaltose recipients had significantly higher median Hb at 6 months compared to iron sucrose (12.4 vs 11.6 g/dL, p = 0.045).

Conclusions:

Although our small retrospective cohort limits definitive conclusions, trends suggest that newer IV iron formulations may provide more effective correction of IDA post-bariatric surgery than iron sucrose—consistent with practice guidelines to use one- to two-dose regimens. Additionally, hypophosphatemia developed in two vitamin D deficient patients following treatment with iron sucrose or ferric carboxymaltose, highlighting the need for careful post-treatment monitoring. Finally, the exclusive inclusion of female patients may reflect sex-specific risk for refractory IDA, or the predominance of women in the bariatric population. Further research with larger patient groups for each IV formulation is needed to clarify differences in efficacy and safety in this population.