Beta Thalassemia (2)

Individuals who have Beta thalassemia trait have microcytosis and hypochromia; there may be targetting, elliptocytosis, though some individuals have an almost normal smear. Hemoglobins A₂ and F will be elevated on hemogram results. These hematologic features can be accentuated in women with trait who are pregnant and in individuals who are folate or iron deficient. If iron deficiency is concurrent with beta thalassemia trait there may be a normal Hgb A₂. Iron deficiency causes decreased hemoglobin production, and folate or vitamin B₁₂ deficiency can lead to megaloblastic anemia with increased Hgb A₂. Both of these deficiencies need to treated prior to evaluation for thalassemia trait. In iron, B₁₂, and folate replete individuals, the Hgb A₂ can be as high as 3.5 to 8% and the Hgb F as high as 1 to 5%. Generally, beta thalassemia trait is milder in African-Americans (who frequently have a promoter gene mutation) but has a similar presentation in individuals of Chinese, Southeast Asian, Greek, Italian, and Middle Eastern heritage.

Infants born in 42 of the 50 states in the United States with newborn screening programs will be diagnosed as having a hemoglobin disorder. In states without newborn screening for hemoglobinopathies and in recent immigrants to this country, affected children are frequently identified outside the newborn period, and the evaluation of their microcytic anemia includes differentiation between iron deficiency and beta thalassemia trait. The red blood cell indices can be helpful in this differentiation, as the hemoglobin concentration and the red cell count will generally be lower in iron deficiency. The distinguishing finding in beta thalassemia is a hemoglobin electrophoresis with the finding of elevated Hgb A₂ and F. Both will be increased in beta thalassemia trait without iron deficiency, and will be normal or decreased in alpha thalassemia and isolated iron deficiency anemia. There are several formulas to help in office screening, but they are also based on the assumption that the child is not iron deficient. Usually iron deficiency can be ruled out using free erythrocyte protoporphyrin (FEP), transferrin saturation or ferritin as a screening test in children who have a hypochromic microcytic anemia. The least expensive test is a trial of iron and a repeated hemogram after a month. A lead level should be obtained if there is an index of suspicion for lead toxicity.

Diagnostic challenges can still arise: if both alpha and beta thalassemia coexist, the changes in Hgb A₂ and F will not be apparent, and as noted above, there are instances of normal or elevated levels of Hgb A₂ and F in beta thalassemia trait. Family studies and, if warranted, DNA analysis can be used to make a definitive diagnosis. <next>

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