What is the ferritin level in ng/mL indicative of iron deficiency anemia?

Ferritin Levels in Iron Deficiency Anemia

Serum ferritin levels below 30 ng/mL without inflammation, or below 100 ng/mL in the presence of inflammation, are diagnostic of iron deficiency anemia. 1

Diagnostic Criteria for Iron Deficiency Anemia

Iron deficiency anemia is diagnosed using multiple parameters, with serum ferritin being the most sensitive test for evaluating iron stores:

• Without inflammation:

  • Ferritin < 30 ng/mL indicates iron deficiency 1, 2

• With inflammation/chronic disease:

  • Ferritin < 100 ng/mL may indicate iron deficiency 1, 3
  • C-reactive protein (CRP) should be measured to assess inflammatory status

• Additional parameters:

  • Transferrin saturation (TSAT) < 20% 3, 1
  • Low serum iron
  • Elevated total iron binding capacity (TIBC)
  • Typically microcytic (low MCV) and hypochromic red cells

Special Considerations

Population-Specific Variations

• Healthy subjects without comorbidities:

  • Absolute iron deficiency: ferritin < 12 ng/mL with TSAT < 16% 3

• Chronic Kidney Disease patients:

  • Absolute iron deficiency: ferritin < 100 ng/mL with TSAT < 20% 3
  • Functional iron deficiency may occur with normal or elevated ferritin

• Cancer patients:

  • Functional iron deficiency may occur with TSAT between 20-50% and ferritin between 30-800 ng/mL 3

Limitations of Current Diagnostic Thresholds

• Recent evidence suggests that the traditional ferritin cutoff may lead to underdiagnosis of iron deficiency in women 4
• Some studies suggest a physiologic ferritin "cutoff" of 50 ng/mL may be more appropriate 4
• In community-dwelling older adults, a cutoff of 22 μg/L has been proposed 5

Pitfalls in Diagnosis

• Ferritin as an acute phase reactant:

  • Inflammation, infection, or malignancy can elevate ferritin levels despite iron deficiency 1, 6
  • In these cases, using a higher cutoff (100 ng/mL) improves diagnostic accuracy

• Functional iron deficiency:

  • Can occur despite normal ferritin levels, especially in patients receiving erythropoietin therapy 3
  • Characterized by inadequate iron supply for erythropoiesis despite adequate iron stores

• Distinguishing from anemia of chronic disease:

  • Both conditions can present with low TSAT < 20% and ferritin 100-700 ng/mL 3
  • Inflammatory markers and response to iron therapy help differentiate

Clinical Approach

1. Measure serum ferritin, TSAT, and CRP
2. Interpret ferritin based on inflammatory status:
   • No inflammation: < 30 ng/mL indicates iron deficiency
   • With inflammation: < 100 ng/mL indicates iron deficiency
3. Consider additional testing (soluble transferrin receptor, bone marrow examination) in cases with ferritin between 30-100 ng/mL without clear evidence of inflammation 1

Iron deficiency anemia is common, affecting approximately 1.2 billion people worldwide, including 10 million in the US 2. Early diagnosis and treatment can significantly improve patient outcomes and quality of life.