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Fetal hemoglobin (Hb F) consists of two alpha and two gamma chains. It is the major hemoglobin of the fetus and newborn, comprising 60 to 90% of total hemoglobin. By 24 months of age, Hb F levels decrease to adult levels of 0 - 2% of the total hemoglobin; however, a few individuals may have slightly higher levels (5%) for 2 3 years. Fetal hemoglobin may be elevated in beta thalassemia, hereditary persistence of fetal hemoglobin (HPFH), and several hemoglobinopathies including sickle cell anemia. In heterozygous beta thalassemia, Hb F may be slightly increased to 2.1-5.0%, and in homozygous beta thalassemia is elevated to between 10 and 90%. In homozygous HPFH, the Hb F level is 100% and in heterozygous HPFH (in Blacks) is usually between 15 35%. Elevated Hb F levels may also be seen in acquired disorders such as megaloblastic anemia, myelofibrosis, leukemias and pregnancy. Hb F may also be useful in the detection of fetomaternal bleeding (see Kleihauer Bettke). Reference range in adults is 0 - 2%. Specimen requirement is one lavender top (EDTA) tube of blood. |
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