Question:medium
A 16 year old girl presents with a history of fatiguability, weakness and lethargy. The complete blood count (CBC) reveals a haemoglobin of 7.0 g/dL, MCV of 70 fL, MCH of 20 pg/cell and a red cell distribution width (RDW) of 20. The most likely diagnosis is:
A 16 year old girl presents with a history of fatiguability, weakness and lethargy. The complete blood count (CBC) reveals a haemoglobin of 7.0 g/dL, MCV of 70 fL, MCH of 20 pg/cell and a red cell distribution width (RDW) of 20. The most likely diagnosis is:
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High RDW with microcytosis favours iron deficiency over thalassaemia trait.
Updated On: Jun 24, 2026
- Iron deficiency anaemia
- Thalassaemia minor
- Thalassaemia major
- Sickle cell trait
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The Correct Option is A
Solution and Explanation
The cell size data tell most of the story. With MCV 70 and MCH 20 the red cells are small and pale, so we are choosing among the microcytic causes: iron deficiency, thalassaemia minor, thalassaemia major and to a lesser extent some others.
The deciding number is the RDW of 20, which is clearly raised. RDW reflects how unequal the red cells are in size. Iron deficiency raises RDW because the marrow produces a mix of normal and progressively smaller cells as stores fall. By contrast, thalassaemia trait gives a uniform population of small cells, so its RDW tends to be normal. A high RDW thus tilts the diagnosis firmly toward iron lack rather than a thalassaemia trait.
The two remaining choices also fit poorly. Thalassaemia major would have declared itself in infancy with severe transfusion-dependent anaemia, not as a new teenage complaint. Sickle cell trait carries an essentially normal blood film. A 16 year old girl with menstrual blood loss developing microcytic anaemia with high anisocytosis is the textbook picture of iron deficiency.
\[\boxed{\text{A. Iron deficiency anaemia}}\]
The deciding number is the RDW of 20, which is clearly raised. RDW reflects how unequal the red cells are in size. Iron deficiency raises RDW because the marrow produces a mix of normal and progressively smaller cells as stores fall. By contrast, thalassaemia trait gives a uniform population of small cells, so its RDW tends to be normal. A high RDW thus tilts the diagnosis firmly toward iron lack rather than a thalassaemia trait.
The two remaining choices also fit poorly. Thalassaemia major would have declared itself in infancy with severe transfusion-dependent anaemia, not as a new teenage complaint. Sickle cell trait carries an essentially normal blood film. A 16 year old girl with menstrual blood loss developing microcytic anaemia with high anisocytosis is the textbook picture of iron deficiency.
\[\boxed{\text{A. Iron deficiency anaemia}}\]
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