Ferritin: A Key Biomarker of Iron Status
Ferritin is a protein that serves as the primary storage form of iron in the body, with serum ferritin being the most useful single marker for assessing total body iron stores. 1
What is Ferritin?
Ferritin is primarily an intracellular protein found in:
- Liver
- Spleen
- Bone marrow reticuloendothelial cells
While most ferritin is intracellular, a small amount circulates in plasma. Under normal conditions, there is a direct relationship between serum ferritin concentration and total body iron stores, with 1 μg/L of serum ferritin approximately equivalent to 10 mg of stored iron 2.
Clinical Significance of Ferritin Measurement
Diagnostic Value
- Iron Deficiency: Serum ferritin levels <15 μg/L indicate definitive iron deficiency, with a specificity of 99% 1
- Low Iron Stores: Levels <30 μg/L indicate low body iron stores 1
- Iron Overload: Levels >200-300 μg/L may indicate iron overload conditions 2
Interpretation Considerations
- Ferritin functions as an acute phase reactant, increasing during inflammation, infection, and tissue damage 2
- In inflammatory conditions, ferritin may be elevated despite actual iron deficiency 2
- Serum ferritin reflects both reticuloendothelial system and parenchymal iron stores 2
Ferritin in Clinical Practice
Advantages of Ferritin Testing
- More sensitive than hemoglobin for detecting early iron deficiency 2
- Low values are highly specific for iron deficiency 2
- Can distinguish differences in iron stores within the physiological range 3
- Becomes abnormal before exhaustion of mobilizable iron stores and onset of anemia 3
Limitations
- Poor specificity when elevated due to its role as an acute phase reactant 2, 4
- In inflammatory conditions, only 10% of hyperferritinemia cases relate to actual iron overload 4
- May be elevated in various conditions unrelated to iron status:
Optimal Use in Clinical Assessment
For accurate assessment of iron status:
- Combine ferritin measurement with other iron parameters:
Special Clinical Scenarios
- Chronic Inflammatory Conditions: Consider using higher ferritin cutoffs (up to 100 μg/L) to diagnose iron deficiency 1
- Chronic Kidney Disease: Ferritin may be elevated (100-700 ng/mL) despite functional iron deficiency 2
- Distinguishing Iron Deficiency from Inflammation: Soluble transferrin receptor (sTfR) remains normal in functional iron deficiency but elevates in true iron deficiency 2
Clinical Pitfalls to Avoid
- Don't rely solely on ferritin when inflammation is present
- Don't assume normal ferritin excludes iron deficiency in inflammatory states
- Don't interpret elevated ferritin as iron overload without considering inflammatory causes
- Don't miss iron deficiency by using standard cutoffs in inflammatory conditions
Ferritin measurement provides similar information to bone marrow aspirates stained for iron but is much less invasive 3. When interpreted correctly alongside other iron parameters and clinical context, it serves as an invaluable tool for assessing iron status across the spectrum from deficiency to overload.