Approach Considerations
Thalassemia major is a severe anemia that presents during the first few months after birth, when the patient’s level of fetal hemoglobin decreases. The diagnosis is usually obvious in the clinical setting of appropriate age and ethnic background. In some cases, the brisk erythropoiesis with increased erythroblasts may be mistaken for clonal proliferative disorders such as leukemia or myelodysplasia.
Skeletal abnormalities in patients with longstanding beta thalassemia major include an expanded bone marrow space, resulting in thinning of the bone cortex. These changes are particularly dramatic in the skull, which may show the characteristic “hair-on-end” appearance. [9] Bone changes can also be observed in the long bones, vertebrae, and pelvis.
The liver and biliary tract of patients with thalassemia major may show evidence of extramedullary hematopoiesis and damage secondary to iron overload from multiple transfusion therapy. Transfusion also may result in infection with the hepatitis virus, which leads to cirrhosis and portal hypertension. Gallbladder imaging may show the presence of bilirubin stones.
The heart is a major organ affected by iron overload and anemia. Cardiac dysfunction in patients with thalassemia major includes conduction system defects, decreased myocardial function, and fibrosis. Some patients also develop pericarditis. Cardiac magnetic resonance imaging (MRI) is considered the criterion standard for measuring cardiac indices, as well as for evaluating cardiac overload by measurement of T2* (relaxation parameter), with a cardiac T2* of less than 10 ms being the most important predictor of development of heart failure. [10]
Thalassemia minor usually presents as a mild, asymptomatic microcytic anemia and is detected through routine blood tests in adults and in older children. These laboratory findings should be evaluated as indicated.
Laboratory Studies
The diagnosis of beta thalassemia minor usually is suggested by the presence of the following:
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Mild, isolated microcytic anemia
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Target cells on the peripheral blood smear (see the images below)
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A normal red blood cell (RBC) count
Peripheral smear in beta-zero thalassemia minor showing microcytes (M), target cells (T), and poikilocytes.
Peripheral smear from a patient with beta-zero thalassemia major showing more marked microcytosis (M) and anisopoikilocytosis (P) than in thalassemia minor. Target cells (T) and hypochromia are prominent.
Heinz bodies, which represent inclusions within RBCs consisting of denatured hemoglobin (Hb), may also be seen in the peripheral blood. [11]
Elevation of the Hb A2 level, demonstrated by electrophoresis or column chromatography, confirms the diagnosis of beta thalassemia trait. The Hb A2 level in these patients usually is approximately 4-6%. In rare cases of concurrent severe iron deficiency, an increased Hb A2 level may not be observed, although it becomes evident with iron repletion. The increased Hb A2 level also is not observed in patients with the rare delta-beta thalassemia trait. An elevated Hb F level is not specific to patients with the beta thalassemia trait.
Free erythrocyte porphyrin (FEP) tests may be useful in situations in which the diagnosis of beta thalassemia minor is unclear. The FEP level is normal in patients with the beta thalassemia trait, but it is elevated in patients with iron deficiency or lead poisoning.
Alpha thalassemia is characterized by genetic defects in the alpha-globin gene, and this variant has features similar to beta thalassemia (see Diagnostic Considerations). Patients with this disorder have normal Hb A2 levels. Establishing the diagnosis of the alpha thalassemia trait requires measuring either the alpha-beta chain synthesis ratio or performing genetic tests of the alpha-globin cluster (using Southern blot or polymerase chain reaction [PCR] assay tests).
Iron studies (iron, transferrin, ferritin) are useful in excluding iron deficiency and the anemia of chronic disorders as the cause of the patient's anemia.
Evidence of hemolysis in the form of indirect hyperbilirubinemia, low haptoglobin, and elevated lactate dehydrogenase may be seen as a result of ineffective erythropoiesis and consequent destruction of these RBCs.
Patients may require a bone marrow examination to exclude certain other causes of microcytic anemia. Physicians must perform an iron stain (Prussian blue stain) to diagnose sideroblastic anemia (ringed sideroblasts).
The Mentzer index is defined as mean corpuscular volume per red blood cell count. An index of less than 13 suggests that the patient has the thalassemia trait, and an index of more than 13 suggests that the patient has iron deficiency. [8]
Prenatal Diagnosis
Prenatal diagnosis is possible through analysis of DNA obtained via chorionic villi sampling at 8-10 weeks’ fetal gestation or by amniocentesis at 14-20 weeks’ gestation. In most laboratories, the DNA is amplified using PCR and then is analyzed for the presence of the thalassemia mutation using a panel of oligonucleotide probes corresponding to known thalassemia mutations.
Since the genetic defects are quite variable, family genotyping usually must be completed for diagnostic linkage (segregation) analysis. With the anticipated availability of large-scale mutation screening by DNA chip technology, extensive pedigree analyses may be obviated.
Physicians can perform fetal blood sampling for Hb chain synthesis at 18-22 weeks’ gestation, but this procedure is not as reliable as DNA analysis sampling methods. Genetic therapy strategies are currently in the early stages of development.
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Peripheral smear in beta-zero thalassemia minor showing microcytes (M), target cells (T), and poikilocytes.
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Peripheral smear from a patient with beta-zero thalassemia major showing more marked microcytosis (M) and anisopoikilocytosis (P) than in thalassemia minor. Target cells (T) and hypochromia are prominent.
