What does low ferritin level indicate?

What Does Low Ferritin Mean?

Low serum ferritin is the most specific indicator of depleted iron stores in the body and represents an early stage of iron deficiency that can progress to iron-deficiency anemia if left untreated. 1

Interpreting Ferritin Levels

Ferritin is a protein that stores iron in the body, and its concentration in serum directly relates to the amount of iron stored, with 1 μg/L of serum ferritin approximately equivalent to 10 mg of stored iron 1. The interpretation of ferritin levels depends on several factors:

Diagnostic Thresholds

• Without inflammation:

  • Ferritin < 15 μg/L confirms iron deficiency 1
  • Ferritin < 30 μg/L indicates iron deficiency in most clinical contexts 1, 2

• With inflammation/chronic disease:

  • Ferritin < 100 μg/L may indicate iron deficiency 1
  • Ferritin between 30-100 μg/L suggests a combination of true iron deficiency and anemia of chronic disease 1

Normal Reference Ranges

• Men: Average 135 μg/L 1
• Women: Average 43 μg/L 1
• Children (6-24 months): Approximately 30 μg/L 1

Clinical Significance of Low Ferritin

Low ferritin represents depleted iron stores before anemia develops. This condition can cause significant symptoms even without anemia:

• Fatigue and reduced performance 1, 2
• Irritability and depression 2
• Difficulty concentrating 2
• Restless legs syndrome (32-40% of cases) 2
• Pica (40-50% of cases) 2

Diagnostic Approach

When evaluating low ferritin, consider:

1. Confirm iron deficiency status:

   • Check transferrin saturation (iron/TIBC × 100)
   • Values < 16% with low ferritin strongly support iron deficiency 1

2. Assess for inflammation:

   • Measure inflammatory markers (CRP, ESR)
   • Ferritin is an acute-phase reactant and may be falsely elevated in inflammation 1, 3

3. Evaluate for anemia:

   • Check hemoglobin, MCV, RDW
   • Low MCV with high RDW (>14%) suggests iron deficiency anemia 1

Common Causes of Low Ferritin

• Blood loss (menstrual, gastrointestinal) 2
• Impaired iron absorption (atrophic gastritis, celiac disease, bariatric surgery) 2
• Inadequate dietary iron intake 2
• Pregnancy (affects up to 84% of women in third trimester) 2
• Regular blood donation 4

Special Considerations

Obesity and Inflammation

In overweight and obese individuals, ferritin may be elevated due to inflammation despite iron deficiency. In these cases, transferrin saturation is more reliable than ferritin alone 3.

Women's Health

Current laboratory reference ranges may underdiagnose iron deficiency in women, as studies show 30-50% of healthy women have no marrow iron stores 5. Some experts suggest a physiologic ferritin cutoff of 50 ng/mL would be more appropriate 5.

Athletes

Iron deficiency without anemia can negatively impact aerobic performance in athletes. Regular screening is recommended, especially for female athletes who have a 15-35% prevalence of iron deficiency 1.

Treatment Approach

For confirmed iron deficiency:

1. Oral iron supplementation:

   • First-line therapy for most patients 2
   • Ferrous sulfate 325 mg daily or on alternate days 2
   • Monitor response with repeat ferritin and hemoglobin measurements

2. Intravenous iron when indicated:

   • Oral iron intolerance
   • Poor absorption conditions
   • Chronic inflammatory conditions
   • Ongoing blood loss
   • Second and third trimesters of pregnancy 2

3. Address underlying causes:

   • Evaluate for sources of blood loss
   • Assess for malabsorption
   • Optimize dietary iron intake

Low ferritin is an early warning sign of iron depletion that should prompt appropriate evaluation and treatment to prevent progression to iron deficiency anemia and improve quality of life.