Diagnosis of a beta thalassaemia is made on the basis of:
- marked hypochromic, microcytic anaemia; target cells are seen and circulating nucleated red cells are always present; reticulocyte count is usually reduced
- exclusion of iron deficiency, and of anaemia of chronic disease
- haemoglobin electrophoresis - see section relating genotype and phenotype for expected results
- in difficult cases - demonstration of unbalanced alpha and beta globin synthesis in reticulocytes following in vitro pulse labelling with radioactive leucine
- prenatal diagnosis is possible - foetal blood sampling or gene probe analysis of amniotic cells
Diagnosis should be suspected by pre-conception and antenatal screening in at risk patients and established by pre-natal or neonate testing. (1,2)
Iron overload monitoring (1,2)
- can be assessed by calculation annual transfusions expressed in ml/kg/yr of pure red cells, and average daily transfusional iron loading (expressed as mg/ kg/day) and assuming 1 ml of pure red cells contains 1.08 mg of iron. Patients whose iron loads are more than 0.3 mg/kg/day require higher chelation dosing. (1)
- serum ferritin is a helpful guide. Persistently high levels (>2500μg/l) can lead to cardiac complications. But levels at 500-1500 μg/l over the long term carry a relatively low risk. Although levels can fluctuate and complications present even at this level (1).
References:
- Standards for the Clinical Care of Children and Adults with Thalassaemia in the UK, United Kingdom Thalassaemia Society 2016
- Thalassaemia International Federation. A short guide for the management of transfusion-dependent thalassaemia. 2nd ed. 2022 [internet publication].