Are these lab results, including microcytic anemia (low Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin (MCH)), high Red Cell Distribution Width (RDW) (Coefficient of Variation (CV)), and low hemoglobin, consistent with thalassemia in this patient?

Laboratory Findings Suggestive of Iron Deficiency, Not Thalassemia

These laboratory results are most consistent with iron deficiency anemia rather than thalassemia, primarily because of the elevated RDW-CV of 16.9%. 1, 2

Key Discriminating Features

RDW as the Critical Differentiator

• The elevated RDW-CV (16.9%, reference range 11.0-15.0%) strongly indicates iron deficiency anemia rather than thalassemia trait. 3, 1, 2
• In thalassemia trait, the RDW typically remains normal (≤14%) because red blood cells are uniformly small, whereas iron deficiency produces heterogeneous cell populations with both older normal-sized cells and newer microcytic cells. 1, 2
• Classic research demonstrates that in patients with microcytosis (MCV <70 fL), the RDW coefficient of variation was <14.0% in 22 of 25 beta-thalassemia minor patients, but was always >14.0% in all 53 iron deficiency anemia patients. 2

Supporting Laboratory Patterns

• The RBC count of 5.00 m/mm³ (normal range) argues against thalassemia, which typically presents with an elevated RBC count despite microcytosis—the so-called "Mentzer index" pattern where MCV is reduced out of proportion to anemia. 1
• The microcytosis (MCV 72.2 fL) combined with low MCH (22.6 pg) and mild anemia (Hb 11.3 g/dL) fits the classic pattern of iron deficiency. 4

Essential Next Steps to Confirm Diagnosis

Mandatory Iron Studies

• Serum ferritin is the single most powerful test and must be obtained immediately. 4
• A ferritin <30 μg/L confirms iron deficiency in the absence of inflammation; <100 μg/L may still indicate iron deficiency if inflammation is present. 4
• Transferrin saturation should be measured simultaneously with ferritin and CRP to assess for functional iron deficiency. 4, 3

If Iron Studies Are Normal or Equivocal

• Hemoglobin electrophoresis should be performed to definitively exclude thalassemia trait, particularly given the microcytosis. 4, 1
• However, the elevated RDW makes thalassemia highly unlikely—the diagnostic odds ratio for RDW in distinguishing these conditions is only 6.8, the lowest of all discriminant indices, but an RDW >14% still has strong negative predictive value for thalassemia. 5

Clinical Pitfalls to Avoid

• Do not assume thalassemia based solely on microcytosis and normal/near-normal RBC count without checking iron studies first. 4
• The high RDW-CV (16.9%) is the most important clue here—nearly half of thalassemia cases may have elevated RDW, but the degree of elevation seen here (>2 standard deviations above normal) strongly favors iron deficiency. 6, 5
• Combined deficiencies (iron plus folate or B12) can mask each other, but the elevated RDW helps identify this scenario. 4

Recommended Diagnostic Algorithm

1. Order serum ferritin, transferrin saturation, and CRP immediately. 4, 3
2. If ferritin confirms iron deficiency (<30 μg/L), investigate the source (gastrointestinal blood loss, dietary inadequacy, malabsorption including celiac disease). 4, 3
3. If ferritin is normal (>100 μg/L), proceed to hemoglobin electrophoresis to exclude thalassemia trait, though this is unlikely given the elevated RDW. 4, 1
4. Consider a therapeutic trial of oral iron (ferrous sulfate 325 mg daily or 65 mg elemental iron daily) and recheck CBC in 4-6 weeks—a hemoglobin rise ≥10 g/L within 2 weeks is highly suggestive of iron deficiency even if initial iron studies were equivocal. 4, 3