What causes high RBC count and low MCV (Mean Corpuscular Volume) in a child with low ferritin and iron saturation levels, indicating iron deficiency anemia?

Diagnosis: Concurrent Iron Deficiency and Beta-Thalassemia Trait

This 5-year-old male child most likely has both iron deficiency and beta-thalassemia trait occurring simultaneously, given the combination of elevated RBC count (characteristic of thalassemia), low MCV of 73 fL (microcytosis), and clear iron deficiency markers (ferritin 21 μg/L and 34% iron saturation).

Diagnostic Reasoning

Why Both Conditions Are Present

• The elevated RBC count with low MCV strongly suggests thalassemia trait, as thalassemia characteristically produces increased red cell production with small cell size 1, 2

• The ferritin of 21 μg/L confirms depleted iron stores, as values <30 μg/L indicate iron deficiency in children without inflammation 2

• The iron saturation of 34% is borderline but combined with low ferritin confirms iron deficiency, particularly when transferrin saturation <20% is typically diagnostic, though 34% with low ferritin still indicates inadequate iron availability 1, 3

• This dual diagnosis occurs in approximately 7% of children with microcytic anemia in regions where both conditions are prevalent 4

Key Distinguishing Features

The RDW value is critical here but was not provided in your case. However, the diagnostic pattern suggests:

• If RDW >14%: This would support concurrent iron deficiency, as iron deficiency causes increased variation in red cell size while thalassemia trait typically shows RDW ≤14% 1

• Thalassemia trait alone would show: Elevated RBC count, low MCV, normal-to-high ferritin (>30 μg/L), and normal-to-low RDW 2

• Iron deficiency alone would show: Normal-to-low RBC count, low MCV, elevated RDW, and low ferritin 2

Recommended Diagnostic Workup

Immediate Next Steps

• Check RDW to assess red cell size variation - this will help confirm the dual diagnosis versus isolated thalassemia 1

• Obtain hemoglobin electrophoresis or high-performance liquid chromatography (HPLC) to definitively diagnose beta-thalassemia trait by demonstrating elevated HbA2 (>3.5%) 2

• Measure reticulocyte hemoglobin content (CHr) if available, as CHr <26 pg is the strongest predictor of iron deficiency in children 3

Important Caveats

• Do not assume this is simple iron deficiency based solely on low ferritin - the elevated RBC count is atypical for isolated iron deficiency and mandates thalassemia evaluation 4

• Thalassemia carriers can develop iron deficiency, and approximately 5.5-7% of children with microcytic anemia have both conditions coexisting 5, 4

• Iron therapy will only correct the iron deficiency component - the microcytosis and elevated RBC count from thalassemia trait will persist after iron repletion 5

Management Approach

Iron Supplementation

• Initiate therapeutic iron supplementation (3-6 mg/kg/day of elemental iron) to correct the documented iron deficiency based on low ferritin 1

• Reassess hemoglobin and iron parameters after 8-12 weeks of iron therapy to confirm response 1

• Expect partial improvement only - hemoglobin may increase but MCV will remain low if thalassemia trait is confirmed 5

Genetic Counseling Considerations

• If hemoglobin electrophoresis confirms beta-thalassemia trait, provide genetic counseling and recommend partner screening if family planning is relevant 2

• Document the thalassemia diagnosis clearly to prevent unnecessary future iron supplementation once iron stores are repleted 5

Monitoring Strategy

• After iron repletion, the persistent microcytosis (low MCV) with elevated RBC count and normal ferritin will confirm thalassemia trait 1, 2

• Avoid chronic iron supplementation beyond correction of deficiency, as thalassemia carriers do not benefit from ongoing iron and risk iron overload 5