Iron deficiency anemia Investigation Diagnostic criteria Define anemia as a Hgb concentration below the LLN for the relevant population and laboratory performing the test. B Recognize that a good response to iron therapy (Hgb rise 10 g/L within a 2-week timeframe) in anemic patients is highly suggestive of absolute iron deficiency, even if the results of iron studies are equivocal. B Iron studies Obtain iron studies to confirm iron deficiency before proceeding to other investigations. B Obtain serum ferritin as the single most useful marker of IDA. B Consider obtaining other blood tests (such as transferrin saturation) if a false-normal ferritin is suspected. B Hemoglobin electrophoresis Q Does the patient have a microcytic, hypochromic anemia? Q Is the patient at risk for inherited Hgbopathies on the basis of ethnic background? Yes to all Obtain Hgb electrophoresis to avoid unnecessary gastrointestinal investigations in patients of appropriate ethnic background with microcytosis and hypochromia. B No to any General principles Q Does the patient have anemia with evidence of iron deficiency? Yes Evaluate all levels of anemia in the presence of iron deficiency. B No to any General principles Q Does the patient have anemia with evidence of iron deficiency? Yes Evaluate all levels of anemia in the presence of iron deficiency. B No Consider alternative diagnoses. History and physical examination Q Is there rectal bleeding or tenesmus? Yes Perform a rectal examination. No Consider postponing DRE until after colonoscopy in the absence of rectal symptoms (such as rectorrhagia and tenesmus), as it is rarely contributory. Screening for celiac disease Obtain screening for celiac disease in the initial evaluation of patients with confirmed IDA. B Obtain screening for celiac disease routinely with serologic testing, or on small bowel biopsy at the time of upper gastrointestinal endoscopy. A Urinalysis and microscopy Obtain urinalysis or urine microscopy in the initial evaluation of patients with confirmed IDA. B Upper and lower gastrointestinal investigations Perform upper and lower gastrointestinal endoscopy in the initial evaluation of appropriate patients with confirmed IDA. B Perform upper and lower gastrointestinal endoscopy as first-line gastrointestinal investigations in male and postmenopausal female patients with newly diagnosed IDA. B Consider obtaining CT colonography as a reasonable alternative in patients not suitable for lower gastrointestinal endoscopy. B Insufficient evidence to recommend invasive investigations in non-anemic patients with iron deficiency unless there are additional indications, but consider obtaining periodic blood count monitoring in these patients. I Small bowel investigations BSG Q Does the patient have symptoms suggestive of small bowel disease? Q Does anemia persist despite iron therapy? Yes to any Obtain further investigation of the small bowel and renal tract to exclude other causes in patients with negative bidirectional endoscopy of acceptable quality and either an inadequate response to iron replacement therapy or recurrent IDA. B Perform capsule endoscopy as the preferred investigation for examining the small bowel in patients with IDA, as it is highly sensitive for mucosal lesions. A Consider obtaining CT/MR enterography in patients not suitable for capsule endoscopy and as complementary investigations in the assessment of inflammatory and neoplastic disease of the small bowel. B Consider obtaining further gastrointestinal investigations after a negative capsule endoscopy of acceptable quality only if there is ongoing IDA after iron replacement therapy. B No to all Consider not performing direct visualization of the small bowel unless there are symptoms suggestive of small bowel disease, or if the Hgb cannot be restored or maintained with iron therapy. D