Hemoglobin F, Hemoglobin Variants
Hemoglobin is made up of heme (the iron-containing portion of hemoglobin) and globin (amino acid chains that form a protein). Hemoglobin (Hgb) molecules are found in all red blood cells. They bind oxygen in the lungs, carry the oxygen throughout the body, and release it to the body's cells and tissues. Hemoglobin F is the primary hemoglobin produced by the fetus, and its role is to transport oxygen efficiently in a low oxygen environment. Production of Hgb F stops at birth and decreases to adult levels by 1-2 years of age. Hgb F may be elevated in several congenital disorders: levels can be normal to increased in beta thalassemia; often, levels are increased in individuals with sickle cell anemia and in sickle cell- beta thalassemia. Individuals with sickle cell disease and increased Hgb F often have a milder disease, as the F hemoglobin inhibits sickling of the red cells. Hgb F levels are also increased in a rare condition called hereditary persistence of fetal hemoglobin (HPFH). This is a group of inherited disorders in which Hgb F levels are increased with no hematological or clinical features of thalassemia. Different ethnic groups have different mutations causing HPFH. Hgb F can also be increased in some acquired conditions involving impaired red blood cell production. Leukemias and other myeloproliferative disorders often are also associated with elevated HgbF.
Normal hemoglobin types include:
Hemoglobin A (about 95% - 98%): Hgb A contains two alpha (α) chains and two beta (β) chains
Hgb A2 (2% - 3%): has two alpha (á) and two delta (ä) chains
Hgb F (up to 2%): the primary hemoglobin produced by the fetus during gestation; its production usually falls to a low level shortly after birth; Hgb F has two alpha (α) and two gamma (γ) chains
Hemoglobin variants are abnormal forms of hemoglobin that occur when changes (point mutations, deletions) in the globin genes cause changes in the amino acids that make up the globin protein. These changes may affect the structure of the hemoglobin, its behavior, its production rate, and/or its stability. Several hundred hemoglobin variants have been documented; however, only a few are common and clinically significant. The majority of these are beta chain variants.
These variants are inherited in an autosomal recessive fashion. A person inherits one copy of each beta globin gene from each parent. If one normal beta gene and one abnormal beta gene are inherited, the person is said to be a carrier or to be heterozygous for the abnormal hemoglobin. The abnormal gene can be passed on to any offspring but does not cause symptoms or health concerns in the carrier.
If two abnormal beta genes of the same type are inherited, the person is considered to have the disease and is homozygous for the abnormal hemoglobin. A copy of the abnormal beta gene will be passed on to any offspring.
If two abnormal beta genes of different types are inherited, the person is doubly or compound heterozygous. One of the abnormal beta genes will be passed on to each offspring.
MEANING OF TEST
Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.
OBTAINING THE TEST RESULTS
It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.