Microcytic Anemia in a 5-Year-Old: Iron Deficiency Anemia vs. Beta-Thalassemia Trait
This 5-year-old girl has microcytic anemia (MCV 67.8 fL, MCH 20.6 pg) with borderline hemoglobin (11.1 g/dL) and elevated RDW (16.9%), which strongly suggests iron deficiency anemia rather than beta-thalassemia trait. 1, 2
Diagnostic Reasoning
The laboratory pattern points toward iron deficiency based on:
Low MCV (67.8 fL) with elevated RDW (16.9%): This combination is characteristic of iron deficiency anemia, where red cells show marked size variation 2, 3. Beta-thalassemia trait typically presents with low MCV but normal or only slightly elevated RDW 1, 4.
Hemoglobin 11.1 g/dL: While borderline for a 5-year-old (normal >11.5 g/dL for this age), this represents mild anemia 5. The CDC notes that iron deficiency anemia in preschool children causes developmental delays and behavioral disturbances when hemoglobin falls below 10.5 g/dL, making early detection critical 5.
Low MCH (20.6 pg) and MCHC (30.4 g/dL): These hypochromic indices support iron deficiency, as inadequate iron leads to underproduction of hemoglobin-containing compounds 5, 2.
Required Diagnostic Workup
Obtain serum ferritin immediately to confirm iron deficiency 1, 2:
- Ferritin <30 μg/L confirms depleted iron stores in children without inflammation 1
- If ferritin is equivocal (30-100 μg/L), add transferrin saturation; <20% confirms iron deficiency 2
Order hemoglobin electrophoresis or HPLC to definitively rule out beta-thalassemia trait 1:
- Beta-thalassemia trait shows elevated HbA2 >3.5% 1
- This is essential because both conditions can coexist, and the elevated RDW suggests concurrent iron deficiency even if thalassemia trait is present 1
Check complete blood count with RBC count 1, 2:
- Iron deficiency: normal or low RBC count 2
- Beta-thalassemia trait: characteristically elevated RBC count despite low MCV 1, 2
Management Algorithm
If Iron Deficiency Confirmed (Ferritin <30 μg/L):
Initiate therapeutic iron supplementation at 3-6 mg/kg/day of elemental iron 1:
- This dosing is recommended by the American Academy of Pediatrics for documented iron deficiency in children 1
- Continue for 8-12 weeks, then reassess hemoglobin and iron parameters 1
Investigate underlying cause 5:
- In children not on erythropoietic agents without obvious blood loss, iron deficiency warrants careful assessment for gastrointestinal bleeding 5
- Evaluate dietary history for inadequate iron intake, which is common in children aged 9-18 months but can persist 5
- Consider lead exposure screening, as iron deficiency increases gastrointestinal absorption of heavy metals 5
If Both Iron Deficiency and Beta-Thalassemia Trait Present:
Treat the iron deficiency with supplementation 1:
- Expect partial improvement only: hemoglobin may increase but MCV will remain low if thalassemia trait is confirmed 1
- Document thalassemia diagnosis clearly to prevent unnecessary future iron supplementation once stores are repleted 1
Provide genetic counseling 1:
- Recommend partner screening if family planning is relevant 1
- Avoid chronic iron supplementation beyond correction of deficiency, as thalassemia carriers do not benefit from ongoing iron and risk iron overload 1
Critical Pitfalls to Avoid
Do not assume thalassemia trait based solely on low MCV: The elevated RDW (16.9%) is the key discriminator here, as thalassemia trait typically shows normal RDW 1, 2, 4. Iron deficiency causes heterogeneous red cell populations (high RDW), while thalassemia produces uniformly small cells (normal RDW) 3.
Do not delay iron supplementation while awaiting hemoglobin electrophoresis results: If ferritin confirms iron deficiency, begin treatment immediately 1. Iron deficiency in preschool children causes developmental delays and behavioral disturbances that may persist past school age if not fully reversed 5.
Do not continue chronic iron supplementation if thalassemia trait is confirmed and iron stores are repleted: Thalassemia carriers do not benefit from ongoing iron and risk iron overload 1.