Unit Converter
Ferritin
(Primary Iron Storage Protein – Best Marker for Iron Stores, Iron Deficiency & Inflammation)
Synonyms
- Ferritin
- Serum ferritin
- Iron-storage protein
- Intracellular iron-binding protein
- FTN / FERR
Units of Measurement
- nmol/L
- pmol/L
- µg/L
- µg/dL
- µg/100 mL
- µg%
- ng/mL
Key Conversions
1 ng/mL = 1 µg/L
1 ng/mL = 2.247 pmol/L
1 µg/dL = 10 ng/mL
µg/100 mL = µg% = µg/dL
(Ferritin MW varies by isoform; clinical labs use WHO standard conversion: 1 ng/mL ≈ 2.247 pmol/L)
Description
Ferritin is the main intracellular iron storage protein, found primarily in:
- Liver
- Spleen
- Bone marrow
- Reticuloendothelial system
A small amount circulates in serum.
Serum ferritin directly reflects body iron stores, making it the best test for iron deficiency.
Ferritin also behaves as an acute-phase reactant, increasing in inflammation.
Physiological Role
Ferritin stores iron in a safe, non-toxic form and releases it in a controlled manner for:
- Hemoglobin synthesis
- Myoglobin production
- Enzyme systems
- Cellular metabolism
Ferritin increases with inflammation via IL-6–mediated upregulation.
Clinical Significance
Low Ferritin (Most Important)
Low ferritin = Iron deficiency until proven otherwise.
Causes:
- Nutritional iron deficiency
- Chronic blood loss
- Menstruation
- Pregnancy
- Malabsorption (celiac, IBD)
- Bariatric surgery
- Hookworm infection
- Chronic diseases affecting intake/absorption
Symptoms:
- Fatigue
- Pallor
- Hair loss
- Restless legs
- Pica
- Weakness
Ferritin < 15 ng/mL → Diagnostic of iron deficiency
Ferritin < 30 ng/mL → Strongly suggests deficiency even with inflammation
High Ferritin
Ferritin rises due to:
- Iron overload
- Inflammation
- Liver disease
- Malignancy
1. Iron Overload Disorders
- Hemochromatosis
- Multiple transfusions
- Thalassemia major
- Sideroblastic anemia
2. Inflammation / Infection
Ferritin is an acute-phase reactant → rises in:
- Chronic infections
- Autoimmune diseases
- CKD
- Rheumatologic conditions
3. Liver Disease
High ferritin due to hepatocyte leakage:
- Alcoholic liver disease
- NAFLD/NASH
- Cirrhosis
4. Malignancies
- Leukemia
- Lymphoma
- Solid tumors
5. Critical Illness
Extremely high levels (>10,000 ng/mL) seen in:
- HLH (hemophagocytic lymphohistiocytosis)
- MAS (macrophage activation syndrome)
- Severe sepsis
- COVID-19 cytokine storm
Reference Intervals
(Tietz 8E + WHO + AACE + Mayo + ARUP)
Adults
| Group | Reference Range |
| Men | 30 – 400 ng/mL |
| Women (premenopausal) | 15 – 150 ng/mL |
| Women (postmenopausal) | 30 – 300 ng/mL |
Children
| Age | Ferritin |
| 1–5 years | 10 – 60 ng/mL |
| 6–15 years | 10 – 100 ng/mL |
| Adolescents | 15 – 150 ng/mL |
(Ranges depend on lab assay & population.)
Clinical cutoffs
- <15 ng/mL → iron deficiency
- <30 ng/mL → probable iron deficiency
- >300–400 ng/mL → consider iron overload
- >1000 ng/mL → significant iron overload or severe inflammation
- >10,000 ng/mL → think of HLH/MAS
Diagnostic Uses
1. Best Test for Iron Deficiency
Ferritin is the first-line investigation.
2. Iron Overload Disorders
Used with:
- Transferrin saturation
- Serum iron
- Genetic testing (HFE mutations)
3. Inflammatory Diseases
Interpret cautiously - inflammation raises ferritin.
4. Monitoring Iron Therapy
Ferritin guides:
- Oral iron therapy duration
- IV iron therapy adequacy
5. Critical Illness Marker
Very high ferritin suggests:
- HLH
- Sepsis-associated inflammation
- MAS
Analytical Notes
- Immunoassays commonly used
- Hemolysis minimally affects ferritin
- Inflammation increases ferritin → check CRP concurrently
- Pregnancy reduces ferritin due to increased iron demand
Clinical Pearls
- Ferritin is the earliest marker to fall in iron deficiency - even before hemoglobin drops.
- Ferritin <30 ng/mL is highly sensitive for iron deficiency in adults.
- High ferritin does not always mean iron overload; inflammation is the most common cause.
- Always interpret ferritin with CRP, transferrin saturation, and iron studies.
- Ferritin >10,000 ng/mL is a red-flag for HLH/MAS.
Interesting Fact
Each ferritin molecule can store up to 4500 iron atoms, making it the body’s most efficient iron reservoir.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Iron Metabolism.
- WHO Guidelines - Iron Deficiency Assessment.
- AACE/ACE Clinical Practice Guidelines - Iron Disorders.
- BCSH Hematology Standards - Iron Deficiency.
- Mayo Clinic Laboratories - Ferritin.
- ARUP Consult - Iron Studies Interpretation.
- MedlinePlus / NIH - Ferritin Test.