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FerritinvsIron

Ferritin vs Serum Iron

Understanding the difference between iron storage (ferritin) and circulating iron, and why both are important for diagnosing iron status.

Aspect
Ferritin
Iron
What it measures
Iron storage - the amount of iron stored in your body's tissues
Circulating iron - the amount of iron currently in your bloodstream
Clinical significance
Best single marker for iron deficiency - depletes before anemia develops
Less specific - fluctuates with meals, time of day, and acute illness
When it changes
Depletes slowly over months as stores are used up
Can change rapidly - affected by recent iron intake and inflammation
Optimal range
50-200 μg/L for most people; many feel best at 70-100+
10-30 μmol/L; but single value less meaningful than ferritin
Complicating factors
Elevated by inflammation, infection, liver disease (acute phase reactant)
Very variable day to day; affected by recent food intake

Key Differences

  • •Ferritin shows storage; serum iron shows what's circulating right now
  • •Ferritin is more reliable for diagnosing iron deficiency
  • •Serum iron varies significantly throughout the day; ferritin is stable
  • •Ferritin depletes first in iron deficiency, before serum iron falls
  • •Ferritin can be falsely elevated by inflammation; serum iron drops with inflammation

Why Both Matter

Ferritin and serum iron measure different aspects of iron status, and both are needed for complete assessment. Ferritin represents your iron reserves - like a savings account. Serum iron represents what's currently circulating - like your checking account balance.

Ferritin is generally considered the most useful single marker for iron status because it depletes in early iron deficiency, often before symptoms appear and well before anemia develops. This makes it valuable for early detection and prevention.

However, ferritin has an important limitation: it's an acute phase reactant, meaning it rises with inflammation, infection, and certain diseases. Someone with both iron deficiency and inflammation might have "normal" ferritin that masks their deficiency. In these cases, serum iron and other iron studies (TIBC, transferrin saturation) help clarify the picture.

Serum iron is less reliable as a standalone test because it fluctuates significantly with meals, time of day, and acute illness. However, when combined with TIBC to calculate transferrin saturation, it provides valuable information about iron availability, especially when ferritin interpretation is complicated by inflammation.

Learn more about

Ferritin

A protein that stores iron in your cells.

Learn more about

Iron

An essential mineral required for oxygen transport in the blood.

Frequently Asked Questions

Why is my ferritin normal but I still feel iron deficient?
Ferritin can be falsely elevated by inflammation, masking iron deficiency. Also, many people have symptoms with ferritin in the "normal" range (15-30). Optimal ferritin is typically 50-100+ for symptom resolution.
Should I test iron with ferritin?
A full iron panel (ferritin, serum iron, TIBC, transferrin saturation) is most informative, especially if there's inflammation or unclear results. For routine screening, ferritin alone is often sufficient.
Why does my serum iron vary so much between tests?
Serum iron fluctuates with meals (especially iron-rich foods), time of day (highest in morning), and acute illness. For consistency, test fasting in the morning and not during acute illness.
What if my ferritin is high but serum iron is low?
This pattern suggests inflammation is elevating ferritin while true iron status may be low. Check inflammatory markers (CRP, ESR) and consider the clinical picture. Sometimes this indicates anemia of chronic disease.

Track Both Markers Over Time

Upload your blood test results to BloodTrack and monitor both Ferritin and Iron. See how they change together over time.

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