1. Iron deficiency
   1. Most common cause of anemia
      1. Etiology
         1. Suboptimal oral intake
         2. Poor absorption
         3. Chronic GI blood loss
         4. Other sources
         5. Hb <13 g/dL in men and <12 g/dL in nonpregnant women
   2. Normal total body iron content
      1. 3000-4000 mg
   3. Absorption
      1. Duodenum and proximal jejunum
   4. Daily loss
      1. 1-2 mg
         1. Balanced through intestinal absorption
2. Cutoff value of serum ferritin
   1. 45 ng/mL
      1. Sensitivity for iron deficiency: 85%
      2. Specificity: 92%
   2. Patients with chronic inflammatory conditions or chronic kidney disease.
      1. Ferritin levels don't reflect body iron stores
         1. Other test may be useful
            1. Serum iron, transferrin saturation, soluble transferrin receptor, or C-reactive protein
3. In asymptomatic postmenopausal women and men with iron-deficiency anemia
   1. Bidirectional endoscopy
      1. Lower gastrointestinal malignancy in 8.9%
      2. Upper gastrointestinal malignancy in 2.0%
      3. May be overestimated
         1. Because of referral bias and inclusion of symptomatic as well as asymptomatic patients
4. In asymptomatic premenopausal women with iron deficiency anemia
   1. After a thorough history and physical examination
   2. Bidirectional endoscopy
      1. Lower gastrointestinal malignancy in 0.9%
      2. Upper gastrointestinal malignancy in 0.2%
      3. May be overestimated
         1. Because of referral bias and inclusion of symptomatic as well as asymptomatic patients
5. In patients with iron deficiency anemia without other identifiable etiology after bidirectional endoscopy
   1. Noninvasive testing for H pylori
      1. Associated with atrophic gastritis and hypochlorhydria
         1. Can decrease iron absorption
      2. Treatment of H pylori infection
         1. In conjunction with iron replacement
            1. May lead to improvement in iron deficiency
            2. Compared with those who received iron replacement alone
      3. Recommended over a strategy of routine gastric biopsies at the time of bidirectional endoscopy
6. In uncomplicated asymptomatic patients with iron deficiency anemia and negative bidirectional endoscopy
   1. Trial of initial iron supplementation
      1. Over the routine use of video capsule endoscopy.
         1. Diagnostic yield of VCE finding small bowel malignancy: 1.3%
            1. Very serious risk of bias
   2. Fecal occult blood testing
      1. No evidence
   3. This recommendation does not apply in these cases
      1. Symptoms suggestive of small bowel disease
      2. Anemia refractory to adequate iron supplementation
      3. Hospitalized patients with acute or acute on chronic anemia
7. Other Etiologies
   1. Atrophic gastritis.
      1. The AGA suggests against the use of routine gastric biopsies to diagnose atrophic gastritis
         1. No evidence was found that can affect the clinical management of iron deficiency
   2. Celiac disease
      1. The AGA suggests initial serologic testing, followed by small bowel biopsy only if positive, over routine small bowel biopsies
         1. In asymptomatic adult patients with iron deficiency anemia and plausible celiac disease
            1. Epidemiologic risk factors
            2. Positive family history or personal history of autoimmune diseases
            3. Gastrointestinal symptoms
8. How should iron supplementation be managed?
   1. Daily dose of 150–200 mg of elemental iron
      1. Response is typically evident within 1 month of treatment
   2. Vitamin C co-administration
      1. Evidence is limited
   3. Non-responders
      1. Assessment for nonadherence, malabsorption, or ongoing blood loss