What it measures.
Ferritin is the primary iron storage protein, reflecting your body's iron reserves. However, it's also an acute-phase reactant that rises during inflammation, infection, and malignancy—complicating interpretation. Always evaluate ferritin alongside CRP to distinguish iron status from inflammatory elevation.
The concentration of ferritin in blood, reflecting iron stores. Each ng/mL of ferritin represents approximately 8-10mg of stored iron.
Why it matters.
Low ferritin causes fatigue, hair loss, and poor exercise tolerance even before anemia develops. High ferritin may indicate iron overload (harmful) or inflammation (requires treating underlying cause). Optimal ferritin supports energy and prevents both deficiency and excess.
Physiology.
Iron is stored intracellularly as ferritin, with small amounts released into blood proportional to stores. Ferritin is also an acute-phase reactant—inflammation triggers increased synthesis regardless of iron status. This dual role requires careful interpretation.
Testing & preparation.
How to prepare
- Fasting preferred
- Test in morning for consistency
- Always order with CRP to assess inflammation
- Wait 2+ weeks after acute illness
When to test
Evaluating fatigue, hair loss, exercise intolerance, or as part of comprehensive health assessment. Essential before iron supplementation.
How often
Annually; every 3-6 months if supplementing iron or treating deficiency.
Interpretation.
High ferritin
Common causes:
- Iron overload (hemochromatosis)
- Chronic inflammation (acute phase response)
- Fatty liver disease (common cause)
- Infection or malignancy
- Excessive iron supplementation
- Chronic alcohol use
Implications:
- If CRP elevated: likely inflammatory elevation
- If CRP normal: consider true iron overload
- Hemochromatosis requires genetic testing and phlebotomy
- Very high levels (>1000) warrant investigation
Low ferritin
Common causes:
- Iron deficiency (dietary or blood loss)
- Heavy menstruation
- Gastrointestinal blood loss
- Pregnancy
- Malabsorption (celiac disease)
- Vegetarian/vegan diet without supplementation
Implications:
- Depleted iron stores
- Fatigue, weakness even without anemia
- Hair loss, brittle nails
- Poor exercise tolerance and recovery
- Restless legs syndrome
- Will progress to anemia if not addressed
Optimization.
Diet
- Heme iron from red meat, poultry, fish (best absorbed)
- Non-heme iron from spinach, beans, fortified cereals
- Pair plant iron with vitamin C to enhance absorption
- Avoid calcium, coffee, tea with iron-rich meals
Lifestyle
- Identify and address blood loss sources
- Avoid excessive iron supplementation
- Regular blood donation if levels too high
- Cook in cast iron cookware (modest iron contribution)
Supplements
- Iron supplements only if deficient (ferritin <50 ng/mL)
- Iron bisglycinate is well-absorbed with fewer GI side effects
- Take with vitamin C, away from dairy and coffee
- Avoid iron supplementation if ferritin >150 ng/mL
FAQs.
How do I know if high ferritin is from iron or inflammation?
Check CRP simultaneously. If CRP is elevated, ferritin elevation is likely inflammatory (the body sequesters iron during inflammation as a defense mechanism). If CRP is normal and ferritin is high, consider true iron overload from hemochromatosis or excessive supplementation. Transferrin saturation helps too—it's elevated in iron overload but normal/low in inflammation.
Is iron deficiency without anemia a real problem?
Yes! Iron deficiency without anemia (IDWA) is increasingly recognized as clinically significant. A woman with ferritin of 20 ng/mL may be 'normal' by lab standards but experience significant fatigue, hair loss, and poor exercise tolerance. Research confirms symptoms and quality of life improve with iron supplementation even without anemia. Many functional medicine practitioners consider ferritin <50 ng/mL as suboptimal.