Diagnosis: Non-Anemic Iron Deficiency (NAID)
This patient has non-anemic iron deficiency, characterized by depleted iron stores with preserved hemoglobin levels. 1
Diagnostic Interpretation
The laboratory pattern clearly indicates iron deficiency despite normal hemoglobin:
- Serum iron 8.8 µg/dL: Severely low (normal ~50-170 µg/dL)
- Transferrin saturation 12%: Below the critical 15% threshold that defines iron-deficient erythropoiesis 1, 2
- TIBC 74 µg/dL: Paradoxically low rather than elevated (typically rises in iron deficiency)
- Ferritin 56 ng/mL: Within the diagnostic gray zone for iron deficiency
- Normal hemoglobin: Rules out iron deficiency anemia
Key Diagnostic Reasoning
The transferrin saturation of 12% is the most critical finding here. When transferrin saturation falls ≤15%, it indicates that iron supply to erythropoiesis has become insufficient, defining iron-deficient erythropoiesis (ID grade II) 2. This represents the stage between simple iron depletion and frank anemia.
The ferritin level of 56 ng/mL requires careful interpretation. While above the traditional 30 µg/L threshold for absolute deficiency, British Society of Gastroenterology guidelines suggest that ferritin <45 µg/L provides optimal sensitivity-specificity balance in clinical practice 1. Your patient's ferritin of 56 ng/mL falls just above this, but the severely low transferrin saturation overrides this, confirming functional iron deficiency.
Important Caveats
The unexpectedly low TIBC (74 µg/dL) is atypical. In classic iron deficiency, TIBC typically rises above 45 µmol/L (approximately 250 µg/dL) 3. This discordance suggests:
- Possible concurrent inflammation or chronic disease (which suppresses TIBC)
- Laboratory error or timing issues
- Mixed pathology requiring further evaluation
If inflammation is present, the ferritin may be falsely elevated as an acute phase reactant, masking more severe iron depletion 1. In inflammatory states, ferritin levels up to 100 µg/L can still represent true iron deficiency 4.
Clinical Significance
This represents non-anemic iron deficiency (NAID), where body iron stores are depleted but hemoglobin remains normal 1. The patient has progressed beyond simple iron depletion (grade I) to iron-deficient erythropoiesis (grade II), as evidenced by the transferrin saturation <15% 2.
The combination of transferrin saturation <20% with relatively low ferritin strongly supports the diagnosis, even though the TIBC pattern is atypical 5, 6.
Next Steps
- Investigate underlying cause (GI blood loss, malabsorption, dietary insufficiency, menstrual losses if premenopausal woman)
- Consider checking inflammatory markers (CRP, ESR) to assess whether ferritin is elevated by inflammation
- Initiate iron supplementation to prevent progression to anemia
- GI investigation is generally not warranted in premenopausal women with NAID unless other concerning features are present 1