What is the likely diagnosis and appropriate evaluation for a patient with low mean corpuscular volume, low mean corpuscular hemoglobin, low mean corpuscular hemoglobin concentration, and elevated red blood cell count?

Microcytic Anemia with Elevated RBC Count: Iron Deficiency or Thalassemia Trait

This pattern of low MCV, low MCH, low MCHC with high RBC count most strongly suggests either iron deficiency anemia or thalassemia trait, and you must immediately check serum ferritin to distinguish between them.

Diagnostic Approach

The combination you describe—microcytic, hypochromic indices (low MCV, MCH, MCHC) with elevated RBC count—creates a critical diagnostic fork in the road 1:

First Step: Serum Ferritin

• If ferritin <15-30 μg/L: Iron deficiency anemia is confirmed 1
• If ferritin normal (>30 μg/L) with normal iron studies: Strongly suspect thalassemia trait, particularly beta-thalassemia trait 2, 1

The elevated RBC count is the key distinguishing feature here—this is characteristic of thalassemia trait where the bone marrow compensates for ineffective hemoglobin production by increasing red cell numbers 3, 4.

Critical Distinguishing Features

Beta-Thalassemia Trait Pattern:

• MCV ≤73.8 fL and MCH ≤21.9 pg suggests beta-thalassemia trait over other causes with >90% sensitivity 3
• MCV disproportionately low relative to degree of anemia 1
• RBC count typically elevated (>5.0 million/μL)
• Normal or elevated ferritin
• RDW often normal or only mildly elevated

Iron Deficiency Pattern:

• Any degree of microcytosis possible
• RBC count normal or low (not elevated)
• Ferritin <30 μg/L 1
• RDW typically elevated 5
• Transferrin saturation low

Common Pitfall to Avoid

Do not assume iron deficiency just because indices are low—64% of donors with low MCV and acceptable hemoglobin had iron deficiency, but 36% had hemoglobinopathy alone, and 15% had both conditions simultaneously 4. The elevated RBC count in your case makes thalassemia trait more likely than isolated iron deficiency.

If Ferritin is Normal: Next Steps

When iron studies are normal with this pattern 2, 1:

1. Order hemoglobin electrophoresis/HPLC to identify:

   • Beta-thalassemia trait (elevated HbA2 >3.5%)
   • HbE trait or other variants

2. Consider alpha-thalassemia trait if:

   • Hemoglobin electrophoresis is normal
   • RBC count elevated
   • Iron studies normal
   • Appropriate ethnic background (Southeast Asian, Mediterranean, African descent)

3. Check ethnic background: Thalassemia is more common in Mediterranean, Middle Eastern, Southeast Asian, and African populations 1

If Both Conditions Coexist

Iron deficiency can mask thalassemia trait on hemoglobin electrophoresis 4. If you treat presumed iron deficiency and the microcytosis persists despite ferritin normalization, repeat hemoglobin electrophoresis to unmask underlying thalassemia trait.

Therapeutic Trial

If ferritin is low-normal (20-45 μg/L) and you suspect functional iron deficiency 1:

• A hemoglobin rise ≥10 g/L within 2 weeks of iron therapy confirms iron deficiency even with equivocal iron studies 1
• Lack of response suggests alternative diagnosis

The elevated RBC count in your presentation makes this less likely to be pure iron deficiency and more likely to represent thalassemia trait or combined pathology.