Given hemoglobin 12.1 g/dL, red blood cell count (RBC) 5.33 ×10⁶/µL, mean corpuscular volume (MCV) 73.7 fL, mean corpuscular hemoglobin (MCH) 22.7 pg, mean corpuscular hemoglobin concentration (MCHC) 30.8 g/dL, red cell distribution width (RDW) 14.4 %, and platelets 352 ×10⁹/L, is this iron deficiency anemia or another cause?

Microcytic Anemia Differential: Iron Deficiency vs. Thalassemia Trait

These laboratory values strongly suggest iron deficiency anemia (IDA), but you must obtain serum ferritin to confirm the diagnosis before proceeding with investigation or treatment.

Key Laboratory Findings Analysis

Your patient presents with:

• Microcytosis: MCV 73.7 fL (significantly reduced)
• Hypochromia: MCH 22.7 pg and MCHC 30.8 g/dL (both reduced)
• Mild anemia: Hemoglobin 12.1 g/dL (borderline low for women, normal for men per WHO criteria)
• Elevated RBC count: 5.33 ×10⁶/µL (relatively high despite anemia)
• Mildly elevated RDW: 14.4% (suggests heterogeneous red cell population)

Why This Pattern Favors Iron Deficiency

The combination of microcytosis with hypochromia and mildly elevated RDW is the classic triad for IDA 1. The British Society of Gastroenterology 2021 guidelines emphasize that MCH is actually a more reliable marker than MCV for iron deficiency, as it's less dependent on storage conditions and counting machines 1. Your patient's MCH of 22.7 pg is markedly reduced, strongly supporting iron deficiency.

However, the elevated RBC count (5.33) creates diagnostic ambiguity because this pattern can also occur in beta-thalassemia trait, where patients produce many small red cells 2, 3.

Critical Next Step: Serum Ferritin

You must obtain serum ferritin before making a definitive diagnosis 1. The guidelines are explicit:

• Ferritin <15 μg/L: Highly specific for iron deficiency (99% specificity)
• Ferritin <30 μg/L: Generally indicates low iron stores
• Ferritin <45 μg/L: Optimal cutoff balancing sensitivity and specificity (92% specificity)
• Ferritin >150 μg/L: Essentially rules out absolute iron deficiency, even with inflammation 1

Important Caveat

Ferritin is an acute phase reactant and can be falsely elevated in inflammatory conditions. If ferritin is 45-150 μg/L with clinical suspicion for iron deficiency, consider checking transferrin saturation or C-reactive protein 1.

Distinguishing from Thalassemia Trait

If ferritin is normal or elevated, you must consider beta-thalassemia trait, especially given:

• High RBC count (5.33) relative to the degree of anemia
• Disproportionate microcytosis (MCV 73.7 is quite low for Hb 12.1)

When to Pursue Hemoglobin Electrophoresis

The guidelines recommend Hb electrophoresis in patients with microcytosis and normal iron studies, particularly with appropriate ethnic background (Mediterranean, Middle Eastern, African, Southeast Asian descent) 1.

Recent research shows that MCV ≤73.8 fL and MCH ≤21.9 pg have >90% sensitivity and >80% specificity for beta-thalassemia trait over E-trait 3. Your patient's values (MCV 73.7, MCH 22.7) fall right at this threshold, making thalassemia trait a consideration if iron studies are normal.

Practical Diagnostic Algorithm

1. Order serum ferritin immediately

2. If ferritin <45 μg/L: Diagnose iron deficiency

   • Investigate underlying cause (GI blood loss, menstrual losses, dietary insufficiency, malabsorption)
   • Consider GI investigation at any level of anemia with iron deficiency, especially if Hb <110 g/L (men) or <100 g/L (non-menstruating women) 1

3. If ferritin 45-150 μg/L with high clinical suspicion:

   • Check transferrin saturation (<20% supports iron deficiency)
   • Consider inflammatory markers (CRP, ESR)
   • Trial of iron therapy: Hb rise ≥10 g/L within 2 weeks strongly confirms iron deficiency 1

4. If ferritin >150 μg/L or normal with appropriate ethnic background:

   • Order hemoglobin electrophoresis to evaluate for thalassemia trait
   • Consider other causes of microcytic anemia (chronic disease, sideroblastic anemia)

Common Pitfalls to Avoid

• Don't rely on CBC indices alone for definitive diagnosis—ferritin is essential 1
• Don't assume normal ferritin excludes iron deficiency in inflammatory states—use 45 μg/L cutoff 1
• Don't miss thalassemia trait by treating empirically without confirming iron deficiency—this leads to unnecessary iron therapy and missed genetic counseling opportunities
• Don't forget that RDW is typically elevated in IDA (as in your patient) but normal in thalassemia trait, though this isn't absolute 2, 4

Bottom line: Order ferritin now. If <45 μg/L, treat as IDA and investigate the cause. If normal/elevated, pursue hemoglobin electrophoresis for thalassemia trait.