Interpretation of a Ferritin Level of 21

Understanding Ferritin and Iron Stores

• 1 μg/L of serum ferritin corresponds to approximately 10 mg of stored iron 1
• Average ferritin levels in the US population are:
  • Men: 135 μg/L 1
  • Women: 43 μg/L 1
  • Children (6-24 months): approximately 30 μg/L 1

Clinical Significance of a Ferritin Level of 21

• A ferritin level of 21 μg/L falls below normal ranges for men and is at the lower end of normal for women 1
• This level represents early depletion of iron stores before anemia develops 2
• According to CDC guidelines, ferritin is an early indicator of iron status and the most specific indicator of depleted iron stores 1

Diagnostic Thresholds

• Traditional cutoff for definite iron deficiency: ≤15 μg/L (sensitivity 75%, specificity 98%) 1
• In patients with inflammation, infection, or malignancy, iron deficiency may be present with ferritin levels up to 50 μg/L or even 100 μg/L 3

Clinical Implications

• Additional iron status tests should be considered, including Transferrin saturation (TSAT): values <20% suggest iron deficiency 4, 5
• Complete blood count to assess for anemia and red cell indices 2
• Assessment of inflammatory markers (CRP, ESR) to rule out inflammation that might mask iron deficiency 6

Management Considerations

• Iron supplementation should be considered to replenish iron stores 3
• Oral iron (such as ferrous sulfate 200 mg three times daily) is typically first-line therapy 3
• Treatment should continue for three months after correction of anemia to fully replenish iron stores 3

Important Caveats

• Ferritin is an acute-phase reactant; inflammation, infection, or tissue damage can raise ferritin levels independent of iron status 1
• A "normal" ferritin level in the presence of inflammation may mask iron deficiency 1
• Ferritin levels should be interpreted in conjunction with other iron parameters and clinical context 1, 6