Iron Deficiency Diagnosis and Management
Introduction to Iron Deficiency
- The American Gastroenterological Association strongly recommends using a ferritin cut-off of 45 ng/mL to diagnose iron deficiency in patients with anemia, providing a strong recommendation with high-quality evidence 5
- The British Society of Gastroenterology suggests a ferritin cut-off of 45 μg/L, which provides a respectable specificity of 0.92 and warrants consideration of GI investigation, especially with chronic inflammatory process and anemia 1, 2, 3, 4
Ferritin Thresholds
- Ferritin <15 μg/L is highly specific for absolute iron deficiency, with a specificity of 0.99 1, 2, 3, 4
- Ferritin <30 μg/L generally indicates low body iron stores and represents the lower limit of normal for most laboratories 1, 2, 3, 4
- Ferritin <100 μg/L with elevated CRP/ESR suggests possible iron deficiency in the context of chronic inflammatory conditions 5
Diagnosis and Management
- The British Society of Gastroenterology recommends calculating transferrin saturation (TSAT) to confirm iron deficiency, with TSAT <16-20% confirming iron deficiency (either absolute or functional) regardless of ferritin level 1, 2, 3, 5
- In patients with chronic disease, inflammation, or infection, ferritin levels may appear falsely normal or elevated despite true iron deficiency, and higher ferritin thresholds (<100 μg/L) should be used in these populations 1, 2, 3, 4, 5
Population-Specific Considerations
- In premenopausal women, GI investigation is conditional rather than mandatory for iron deficiency, as menstrual blood loss is the most common cause 1, 2, 3, 4
- In chronic kidney disease patients, absolute iron deficiency is defined as ferritin <100 ng/mL combined with TSAT <20%, and functional iron deficiency occurs when ferritin is 100-700 ng/mL but TSAT remains <20% 5