What are the criteria for diagnosing iron deficiency anemia?

Diagnostic Criteria for Iron Deficiency Anemia

The diagnostic criteria for iron deficiency depend critically on whether inflammation is present: serum ferritin <30 μg/L indicates iron deficiency in patients without inflammation, while ferritin up to 100 μg/L may still represent iron deficiency when inflammation is present. 1, 2

Laboratory Screening Approach

Initial testing should include complete blood count, serum ferritin, and C-reactive protein to assess both anemia and inflammatory status. 1

Definition of Anemia

• Hemoglobin <13 g/dL for men 1
• Hemoglobin <12 g/dL for women 1

Diagnostic Criteria Based on Inflammatory Status

Without Active Inflammation

In patients without clinical, endoscopic, or biochemical evidence of active disease:

• Serum ferritin <30 μg/L is the appropriate diagnostic criterion 1, 2
• Transferrin saturation <16% supports the diagnosis 1
• Serum ferritin <15 μg/L is highly specific (99%) for absolute iron deficiency 2

With Active Inflammation

When inflammation is present (elevated CRP, clinical or endoscopic activity):

• Serum ferritin up to 100 μg/L may still be consistent with iron deficiency 1, 2
• This higher threshold accounts for ferritin being an acute phase reactant that rises with inflammation 1

Mixed Picture (Ferritin 30-100 μg/L with Inflammation)

• If serum ferritin is between 30-100 μg/L in the presence of inflammation, a combination of true iron deficiency and anemia of chronic disease is likely 1, 2
• Transferrin saturation <20% helps confirm iron deficiency in this scenario 1, 2

Anemia of Chronic Disease Criteria

In the presence of biochemical or clinical inflammation:

• Serum ferritin >100 μg/L 1
• Transferrin saturation <20% 1

Additional Supportive Laboratory Findings

Other markers suggestive of iron deficiency anemia include:

• Low mean corpuscular volume (MCV) - microcytic anemia 1
• Raised red cell distribution width (RDW) 1
• Microcytic hypochromic pencil red cells on blood film 1
• Low serum iron 1
• Raised total iron-binding capacity 1

Monitoring Frequency

The frequency of laboratory assessment depends on disease activity:

• Every 6-12 months in patients with remission or mild disease 1
• At least every 3 months in outpatients with active disease 1

Critical Clinical Pitfall

The most common diagnostic error is using a ferritin threshold of <30 μg/L in patients with active inflammation, which will miss iron deficiency in the majority of cases. 1 Ferritin is an acute phase reactant and rises with inflammation, masking underlying iron deficiency. 1 Always assess inflammatory markers (CRP, clinical disease activity) when interpreting ferritin levels. 1