What are the hemoglobin and ferritin levels that indicate the need for an iron infusion in patients with iron deficiency anemia?

Hemoglobin and Iron Levels for Considering Iron Infusion

Iron infusion should be considered when ferritin is <30 ng/mL with TSAT <20% (absolute iron deficiency) or when ferritin is 30-100 ng/mL with TSAT <20% in the presence of inflammation (functional iron deficiency). 1

Diagnostic Parameters for Iron Deficiency

Hemoglobin Thresholds

• Hemoglobin <12 g/dL in women
• Hemoglobin <13 g/dL in men
• Hemoglobin <10 g/dL often triggers consideration for more aggressive iron replacement 1

Iron Studies Indicating Need for IV Iron

1. Absolute Iron Deficiency:

   • Ferritin <30 ng/mL AND
   • Transferrin saturation (TSAT) <20% 1

2. Functional Iron Deficiency:

   • Ferritin 30-100 ng/mL AND
   • TSAT <20% with evidence of inflammation 1
   • In cancer patients, functional iron deficiency may be defined as ferritin 30-800 ng/mL with TSAT 20-50% 1

Specific Clinical Scenarios

Inflammatory Bowel Disease

• Ferritin <100 ng/mL with evidence of inflammation
• IV iron is first-line treatment when:
  • Hemoglobin <10 g/dL
  • Clinically active disease
  • Previous intolerance to oral iron 1

Post-Surgical Patients

• Ferritin <100 ng/mL
• TSAT <20% 1

Cancer-Related Anemia

• Absolute iron deficiency: Ferritin <30 ng/mL with TSAT <20%
• Functional iron deficiency: Ferritin 30-800 ng/mL with TSAT 20-50% 1, 2

Decision Algorithm for Iron Infusion

1. Check hemoglobin and iron studies:

   • Complete blood count with MCV
   • Serum ferritin
   • Transferrin saturation
   • C-reactive protein (to assess inflammation)

2. Consider IV iron if ANY of the following are present:

   • Ferritin <30 ng/mL (regardless of inflammation status) 1
   • Ferritin 30-100 ng/mL with TSAT <20% AND evidence of inflammation 1
   • Hemoglobin <10 g/dL with iron deficiency 1
   • Failed oral iron therapy (inability to increase Hb by 1-2 g/dL within 4 weeks) 3
   • Intolerance to oral iron 4
   • Conditions with impaired oral iron absorption (IBD, post-bariatric surgery) 1
   • Ongoing blood loss exceeding oral absorption capacity 3

Common Pitfalls to Avoid

1. Misinterpreting ferritin in inflammatory states:

   • Ferritin is an acute phase reactant and may be falsely elevated
   • In inflammation, ferritin up to 100 ng/mL may still indicate iron deficiency 1, 3

2. Relying solely on hemoglobin:

   • Normal hemoglobin doesn't exclude iron deficiency
   • Assess iron stores with ferritin and TSAT 3

3. Failing to investigate underlying cause:

   • Always identify and address the source of iron loss or malabsorption 3
   • Consider GI evaluation in appropriate patients 1

4. Overlooking functional iron deficiency:

   • Patients with chronic diseases may have normal ferritin but inadequate iron availability
   • TSAT <20% with ferritin 30-100 ng/mL suggests functional iron deficiency 1

IV iron therapy has been shown to be more effective than oral iron in many clinical scenarios, with faster increases in hemoglobin levels and better patient tolerance 4, 5, 6. Regular monitoring of hemoglobin and iron parameters is essential after treatment to detect recurrent iron deficiency.