Trial of IV vs Oral Iron Treatment of Iron Deficiency Anemia in the Post-Operative Bariatric Surgical Patient

Inclusion criteria: 1. Aged ≥ 18 years 2. Patients who have undergone a Roux-en Y Gastric Bypass or Vertical Sleeve Gastrectomy and are at least 3 months or more out from surgery. 3. Iron deficiency anemia defined as iron deficient with either ferritin\<30 mcg/l, TSAT\<20%, or anemia with Hgb\<13 g/dL for both males and females. 4. Willingness to participate and signing the informed consent form. Exclusion criteria: 1. Iron overload or disturbances in utilization of iron (e.g. hemochromatosis and hemosiderosis) 2. Decompensated liver cirrhosis or active hepatitis (ALAT \> 3 times upper limit of normal) 3. Serum ferritin \> 400 ng/mL or transferrin saturation \>40 % 4. Active acute or chronic infections (assessed by clinical judgment that may be indicated by White Blood Cells (WBC) and C-Reactive Protein (CRP) when these are available) 5. Rheumatoid arthritis with symptoms or signs of active inflammation 6. Pregnant and nursing women 7. History of multiple allergies (two or more) 8. Known hypersensitivity to ferumoxytol or oral iron or any excipients in the drug products 9. Previous IV iron treatment for IDA 10. Other iron treatment or blood transfusion within 4 weeks prior to the screening or treatment visit 11. Planned elective surgery during the study 12. Any other medical condition that, in the opinion of Investigator, may cause the subject to be unsuitable for the completion of the study or place the subject at potential risk from being in the study, e.g. a malignancy, uncontrolled hypertension, unstable ischemic heart disease, or uncontrolled diabetes mellitus