This short case focused on the diagnosis of thalassaemia over iron deficiency. The below factors can help, but there are many overlapping factors and this is more of a guide rather than absolute. Factors that may make this unreliable include co-existing B12/folate deficiency, co-inheritance of alpha thalassaemia trait in addition to beta thalassaemia or use of drugs that alter the MCV e.g. hydroxycarbamide. Thalassaemic disorders are not confined to certain parts of the world. The platelet count may be elevated in iron deficiency. If the MCV is disproportionately low compared to the haemoglobin this also points towatds thalassaemia.
The blood film showed mainly target cells (1). There were occasional spherocytes and some polychromasia. The red cells were small (compared to mature lymphocyte nucleus -2).
The main differential of a low MCV are:
- Iron deficiency
- Anaemia of chronic disease
- Lead poisoning
- Inherited sideroblastic anaemia
She had normal iron stores (ferritin 46μg/l) with no clinical or laboratory evidence of inflammation. Family history revealed her mother was always anaemic. She is from Malaysia.
HPLC revealed a variant haemoglobin in the A2 position. Haemoglobin E runs in this position and this was confirmed on acid and alkaline electrophoresis. The haemoglobin in the A0 time is likely degradation product.
Haemoglobin E is a variant haemoglobin affecting the beta globin gene. There are two beta globin genes and in one is affected by HbE then the patient has HbAE (heterozygous haemoglobin E disease). Homozygous HbE disease is where both beta globin genes are affected and is common in Southeast Asia. It is generally an asymptomatic condition. Patients have mild microcytic anaemia and mild haemolysis. There may be no anaemia at all. They may have mild splenomegaly but this does not usually result in symptoms. The main issue is in pre-pregnancy counselling. Her partner should be tested for any significant haemoglobin disorder. When haemoglobin E is combined with other haemoglobinopathies it can result in a more serious disease – for example if a child inherits haemoglobin E from the mother and an absent/dysfunctional beta globin gene from the father then the child develops HbE/β0 thalassaemia which can be transfusion-dependant.
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