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Simon Senanu: Microcytosis – Iron Deficiency vs Thalassemia
Simon Senanu/LinkedIn
Apr 23, 2026, 16:36

Simon Senanu: Microcytosis – Iron Deficiency vs Thalassemia

Simon Senanu, Medical Laboratory Scientist at Perkins Medical Centre, shared a post on LinkedIn:

“Microcytosis – Iron Deficiency vs Thalassemia

A CBC shows low MCV.

Microcytosis.

The immediate assumption?

Iron deficiency anemia.

But not all microcytosis is iron deficiency – and that distinction matters.

What Is Microcytosis?

Microcytosis refers to:

  • Reduced mean corpuscular volume (MCV)

Typically, <80 fL in adults

It reflects reduced hemoglobin content per cell, resulting in smaller-than-normal RBCs.

The Core Diagnostic Question

When you see microcytosis, always ask:

Is this impaired hemoglobin production or a genetic globin defect?

This distinction separates:

  • Iron deficiency anemia (IDA) from
  • Thalassemia trait Because management differs completely.

Iron Deficiency Anemia (IDA)

Pathophysiology: Inadequate iron leads to reduced heme synthesis, resulting in decreased hemoglobin.

Key Laboratory Features

  • Low MCV (progressive)
  • Low RBC count
  • High RDW (anisocytosis from mixed cell populations)
  • Low ferritin (most specific marker)
  • Low serum iron, high TIBC, low transferrin saturation

Peripheral Smear Clues

  • Microcytosis and hypochromia
  • Marked anisopoikilocytosis
  • Pencil cells / elliptocytes

Cells are small, pale, and variable in size.

Thalassemia Trait

Pathophysiology: Reduced or absent globin chain synthesis (α or β) leads to an Imbalance in globin production, resulting in ineffective erythropoiesis.

Key Laboratory Features

  • Markedly low MCV (often <70 fL)
  • Normal or elevated RBC count
  • Normal RDW (uniform microcytosis)
  • Normal or elevated ferritin and iron

Peripheral Smear Clues

  • Target cells
  • Microcytosis with relatively uniform size
  • Basophilic stippling (in some cases)

Cells are uniformly small despite marked microcytosis and often increased in number.

The Mentzer Index

A Practical Screening Tool

  • Above 13 Suggests iron deficiency
  • Below 13 Suggests thalassemia trait (MCV ÷ RBC count)

Useful for screening but not definitive.

Additional Tests That Refine Diagnosis

  • Serum ferritin: First line for iron status
  • Hemoglobin electrophoresis: Detects β-thalassemia (elevated HbA)
  • CRP: Helps interpret ferritin (as an acute phase reactant)

Interpret iron studies alongside inflammatory markers where relevant.

Diagnostic Pitfalls

  • Coexisting IDA and thalassemia: Masks typical patterns
  • Normal ferritin in inflammation: Can hide iron deficiency
  • Recent iron therapy: Alters lab profile
  • Relying on MCV alone: Oversimplifies diagnosis Microcytosis is a pattern – not a final answer.

Clinical Significance Correct differentiation is essential for:

  • Appropriate treatment (iron vs no iron)
  • Avoiding iron overload in thalassemia
  • Identifying carriers for genetic counseling
  • Preventing repeated misdiagnosis

Laboratory Takeaway Microcytosis is not a diagnosis, it’s a diagnostic pathway.

Always integrate:

  • RBC indices
  • Iron studies
  • Peripheral smear

Clinical context When you see microcytosis, what guides you first RBC count, RDW, or the smear?”

Simon Senanu: Microcytosis - Iron Deficiency vs Thalassemia

Find more posts featuring Simon Senanu on Hemostasis Today.

Health Hematology Hemostasis Hemostasis News Hemostasis Today Iron-Deficiency Mentzer Index Simon Senanu Thalassemia
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