Given a red blood cell count of 5.93 ×10^12/L, mean corpuscular volume of 71.8 fL, mean corpuscular hemoglobin of 21.2 pg, mean corpuscular hemoglobin concentration of 29.6 g/dL, and red cell distribution width of 16.8%, what is the most likely diagnosis and what initial diagnostic and therapeutic steps should be taken?

Microcytic Anemia with Elevated RBC Count: Most Likely Thalassemia Trait

This presentation is most consistent with thalassemia trait (likely beta-thalassemia trait), and you should immediately order serum ferritin, transferrin saturation, and hemoglobin electrophoresis/HPLC to differentiate between iron deficiency anemia and thalassemia.

Understanding the Blood Indices

Your patient presents with:

• Microcytosis (MCV 71.8 fL, normal 80-100 fL) 1
• Hypochromia (MCH 21.2 pg, MCHC 29.6 g/dL - both low)
• Elevated RBC count (5.93 ×10^12/L - notably high)
• Elevated RDW (16.8% - indicating anisocytosis)

The combination of severe microcytosis with an elevated RBC count is the critical distinguishing feature that points toward thalassemia rather than iron deficiency 2.

Diagnostic Algorithm

Step 1: Confirm Iron Status

Order serum ferritin immediately - this is the most powerful test for iron deficiency 2:

• Ferritin <30 μg/L (without inflammation) = iron deficiency 3
• Ferritin <12 μg/L = diagnostic of iron deficiency 2
• Ferritin >100 μg/L = iron deficiency almost certainly excluded 2

Add transferrin saturation:

• <15-16% suggests iron deficiency 1, 4
• <30% may support diagnosis 2

Step 2: Distinguish Thalassemia from Iron Deficiency

Key differentiating features 2, 5:

Feature	Iron Deficiency	Thalassemia Trait
RBC count	Normal or low	Elevated
MCV	Low	Very low (often <75 fL)
RDW	Elevated	Normal or mildly elevated
Ferritin	Low	Normal or elevated

In your case, the elevated RBC count (5.93) with severe microcytosis (71.8 fL) strongly favors thalassemia trait 2.

Step 3: Confirm with Hemoglobin Electrophoresis/HPLC

If ferritin is normal and thalassemia is suspected, order hemoglobin electrophoresis or HPLC 5:

• Beta-thalassemia trait: Elevated HbA2 (>3.5%)
• HbE trait: Presence of HbE band
• Alpha-thalassemia: Normal pattern (requires genetic testing)

Specific cutoffs for beta-thalassemia trait 5:

• MCV ≤73.8 fL with MCH ≤21.9 pg has >90% sensitivity and >80% specificity

Your patient's values (MCV 71.8, MCH 21.2) fall within this range.

Critical Pitfalls to Avoid

1. Do NOT assume iron deficiency based solely on microcytosis - the elevated RBC count argues against this 2

2. Do NOT start empiric iron therapy without confirming iron deficiency - this can mask thalassemia and cause unnecessary iron loading 2

3. Check family history for hemoglobinopathies, especially in patients of Mediterranean, African, Middle Eastern, or Southeast Asian descent 2

4. The elevated RDW (16.8%) can occur in both conditions but is more characteristic of iron deficiency 6, 7. However, combined deficiency states can occur 2

If Iron Deficiency is Confirmed

Should ferritin be low, indicating true iron deficiency:

Investigate the source 2:

• In adult men and postmenopausal women: GI blood loss is the most common cause
• Mandatory evaluation: Upper GI endoscopy with small bowel biopsies (to exclude celiac disease - present in 2-3% of IDA cases) AND colonoscopy or barium enema 2
• Do NOT assume dietary deficiency alone - full GI investigation is required 2

Treatment:

• Oral iron supplementation
• Goal: normalize hemoglobin AND iron stores 3
• Expect ≥2 g/dL hemoglobin increase within 4 weeks 3

If Thalassemia Trait is Confirmed

• No iron supplementation unless concurrent iron deficiency is documented
• Genetic counseling if planning pregnancy
• Family screening may be appropriate
• No specific treatment needed for trait alone