Ferritin of 9 with Normal MCV Still Indicates Significant Iron Deficiency
A ferritin level of 9 μg/L is concerning and indicates iron deficiency regardless of whether the MCV is normal, as ferritin is the most specific indicator of depleted iron stores. 1
Understanding Iron Deficiency Assessment
- Serum ferritin is the most specific test for iron deficiency in the absence of inflammation, with levels <15 μg/L being highly specific (specificity 0.99) for iron deficiency 1
- A ferritin level of 9 μg/L indicates depleted iron stores, as 1 μg/L of serum ferritin concentration is equivalent to approximately 10 mg of stored iron 1
- Normal MCV does not exclude iron deficiency, as MCV has only moderate diagnostic accuracy (area under ROC curve 0.68-0.93) for detecting iron deficiency 2
- In a study of anemic patients, at MCV cutoff limits giving 90% sensitivity for detecting iron deficiency, the specificity was only about 50% 2
Why Normal MCV With Low Ferritin Is Still Concerning
- MCV is a late indicator of iron deficiency and may remain normal in early stages of iron depletion 1
- Iron deficiency progresses through stages, beginning with depletion of iron stores (indicated by low ferritin) before changes in red cell indices occur 1
- Non-anaemic iron deficiency (NAID) represents an initial phase where body iron stores are depleted (hypoferritinaemia) but Hb concentration and possibly MCV remain within normal range 1
- MCH (mean corpuscular hemoglobin) may be a more reliable marker of iron deficiency than MCV, but both have limited sensitivity 1, 3
Clinical Implications
- A ferritin of 9 μg/L requires iron supplementation regardless of MCV status 1
- Iron therapy should be continued for three months after correction of anemia to replenish iron stores 1
- The aim of treatment should be to restore both hemoglobin levels and iron stores to normal 1
- Monitoring should include both hemoglobin and ferritin measurements to ensure complete resolution of iron deficiency 1
Potential Pitfalls and Considerations
- Normal MCV with low ferritin could represent:
- Relying solely on MCV to rule out iron deficiency could lead to missed diagnoses, as studies show MCV, MCH, and MCHC are only moderately accurate in diagnosing empty iron stores 2
- Response to iron therapy is typically robust in true iron deficiency, with significant improvements in hemoglobin, MCV, MCH, and ferritin values within 6 weeks 5
In conclusion, a ferritin level of 9 μg/L represents significant iron depletion that requires treatment regardless of MCV status, as ferritin is a more sensitive and specific indicator of iron stores than red cell indices.