A 28-year-old male from Bangladesh presents with stable anemia over several readings. Currently on iron replacement for iron deficiency anemia.
- What is the significance of his severe microcytosis?
- What laboratory tests would help diagnose the cause of his microcytic anemia?
Click for answer:
Diagnosis: Beta-thalassemia with Hemoglobin E disease
CBC findings suggestive of thalassemia:
(1) High RBC with low MCV, (2) Lack of hypochromasia, (3) Presence of target cells
Q1: What is the significance of his severe microcytosis?
Thalassemia typically has more severe microcytosis than iron deficiency.
Q2: What laboratory tests would help diagnose the cause of his microcytic anemia?
Iron studies and hemoglobin electrophoresis.
Mentzer Index
= MCV/RBC
Index > 13 = iron deficiency
Index < 13 = thalassemia
Thalassemia is the most common monogenic genetic disorder in humans. Thalassemias affects hemoglobin production by disrupting globin synthesis. It is most often found in patients of Mediterranean, Middle East, Indian, and Southeast Asian descent. The severity of thalassemia can range from mild/asymptomatic (trait) to severe, with the latter requiring regular transfusions and iron chelation therapy.
Thalassemia typically has more severe microcytosis than iron deficiency. The Mentzer Index (see Box) uses this feature to help differentiate iron deficiency from beta-thalassemia. Work-up for thalassemia should include iron studies (to exclude concurrent deficiency) and hemoglobin electrophoresis.
CBC Pearls
• Certain forms of thalassemia (e.g. alpha thalassemia trait) cannot be diagnosed by hemoglobin electrophoresis
• Severe microcytosis often suggests thalassemia
Why is the RBC high while the hemoglobin is low?
The RBC count represents the absolute number of erythrocytes in a blood sample. In thalassemia, hemoglobin production is impaired and the body’s physiologic response is to increase RBC production as a compensatory mechanism. This is also the basis for the Mentzer index.