When should I order iron supplementation for iron deficiency anemia?

When to Order Iron Supplementation

Iron supplementation should be ordered when iron deficiency anemia is confirmed, defined as hemoglobin <13 g/dL in men or <12 g/dL in women with evidence of iron deficiency (ferritin <30 ng/mL without inflammation, or <100 ng/mL with inflammation and transferrin saturation <20%). 1

Diagnostic Criteria for Iron Deficiency

Laboratory Screening Requirements

• Order a complete blood count, serum ferritin, and C-reactive protein to screen for iron deficiency anemia 1
• Serum ferritin is the most powerful single test for iron deficiency 1

Ferritin Thresholds Based on Inflammatory Status

Without inflammation (normal CRP):

• Ferritin <30 ng/mL confirms iron deficiency 1
• This applies to patients in clinical remission without biochemical or endoscopic evidence of active disease 1

With inflammation (elevated CRP):

• Ferritin up to 100 ng/mL may still indicate iron deficiency 1
• If ferritin is 30-100 ng/mL with transferrin saturation <20%, a combination of true iron deficiency and anemia of chronic disease is likely 1
• If ferritin >100 ng/mL with transferrin saturation <20%, this indicates anemia of chronic disease 1

Hemoglobin Thresholds for Anemia

• Men: <13 g/dL 1
• Women (postmenopausal): <12 g/dL 1
• Women (premenopausal): <12 g/dL 1
• Pregnant women: varies by trimester (see specific pregnancy thresholds) 1

Monitoring Frequency

For patients with inflammatory bowel disease or chronic disease:

• In remission or mild disease: measure every 6-12 months 1
• Active disease: measure at least every 3 months 1

For general population:

• Premenopausal women: screen every 5-10 years during routine health examinations 1
• Women with risk factors (extensive menstrual blood loss, low iron intake, previous iron deficiency): screen annually 1

Route of Administration Decision

Oral Iron as First-Line

Use oral iron (60-120 mg elemental iron daily) when: 1

• Disease is clinically inactive
• Mild anemia present (hemoglobin 10-12 g/dL)
• No previous intolerance to oral iron
• Patient is not requiring erythropoiesis-stimulating agents

Intravenous Iron as First-Line

Use intravenous iron when: 1

• Clinically active inflammatory bowel disease present
• Hemoglobin <10 g/dL (100 g/L)
• Previous intolerance to oral iron
• Patient requires erythropoiesis-stimulating agents
• Oral iron fails to correct anemia after 4 weeks despite compliance 1

Treatment Goals and Response Monitoring

Target outcomes: 1

• Normalize hemoglobin levels
• Replenish iron stores (ferritin >100 ng/mL)
• Achieve hemoglobin increase of at least 2 g/dL within 4 weeks of treatment 1

Follow-up timing:

• Reassess at 4 weeks after starting treatment 1
• If no response after 4 weeks despite compliance and absence of acute illness, perform additional testing including MCV, RDW, and repeat ferritin 1
• Consider hemoglobinopathies (thalassemia, sickle cell trait) in patients of African, Mediterranean, or Southeast Asian ancestry with anemia unresponsive to iron 1

Critical Pitfalls to Avoid

Do not rely on ferritin alone in inflammatory states: Ferritin is an acute phase reactant and may be falsely elevated in infection, inflammation, or malignancy 1, 2. Always interpret ferritin in context of CRP and transferrin saturation 1.

Do not perform fecal occult blood testing for investigation of iron deficiency anemia—it provides no benefit 1

Do not delay investigation in high-risk patients: Men with hemoglobin <12 g/dL and postmenopausal women with hemoglobin <10 g/dL require urgent investigation for serious underlying pathology, particularly gastrointestinal malignancy 1

All postmenopausal women and all men with confirmed iron deficiency anemia should undergo upper and lower gastrointestinal investigation unless there is significant overt non-GI blood loss 1

Screen all patients for celiac disease regardless of age or sex 1