Study type: Blood collected in a lavender-top [EDTA] tube; related body system: Circulatory/Hematopoietic system. The specimen should be placed in an ice slurry immediately after collection. Information on the specimen label should be protected from water in the ice slurry by first placing the specimen in a protective plastic bag. The specimen should be promptly transported to the laboratory for processing and analysis.

Hgb electrophoresis is a separation process used to identify normal and abnormal forms of Hgb. Electrophoresis and high-performance liquid chromatography as well as molecular genetics testing for mutations can also be used to identify abnormal forms of Hgb. Hgb A is the main form of Hgb in the healthy adult. Hgb F is the main form of Hgb in the fetus, the remainder being composed of Hgb A₁ and A₂. Small amounts of Hgb F are normal in the adult. Hgb C, D, E, H, and S result from abnormal amino acid substitutions during the formation of Hgb and are inherited hemoglobinopathies.

Hgb M is a structural Hgb variant that can be inherited or acquired. It is formed when the heme portion of the deoxygenated Hgb is oxidized to a ferric state rather than to the normal ferrous state, rendering it incapable of combining with and transporting oxygen to tissues. Visible cyanosis can result as levels approach 10% to 15% of total Hgb.

The sickle cell screen is one of several screening tests for a group of hereditary hemoglobinopathies. The test is positive in the presence of rare sickling Hgb variants such as Hgb S and Hgb C Harlem. Electrophoresis and high-performance liquid chromatography as well as molecular genetics testing for beta-globin mutations can also be used to identify Hgb S. Hgb S results from an amino acid substitution during Hgb synthesis whereby valine replaces glutamic acid. Hgb C Harlem results from the substitution of lysine for glutamic acid. Individuals with sickle cell disease have chronic anemia because the abnormal Hgb is unable to carry oxygen. The red blood cells (RBCs) of affected individuals are also abnormal in shape, resembling a crescent or sickle rather than the normal disk shape. This abnormality, combined with cell-wall rigidity, prevents the cells from passing through smaller blood vessels. Blockages in blood vessels result in hypoxia, damage, and pain.

Preconception (maternal and paternal), prenatal, and antenatal hemoglobin electrophoresis screening has become routine practice especially in ethnic populations with a high prevalence for sickle cell anemia, sickle cell disease, and thalassemia in order to detect abnormal hemoglobins. Repeat hemoglobin electrophoresis testing in patients with a known hemoglobinopathy is unnecessary unless it is needed to make a more specific diagnosis or to monitor therapeutic effectiveness.

Knowledge of genetics assists in identifying those who may benefit from additional education, risk assessment, and counseling. Genetics is the study and identification of genes, genetic mutations, and inheritance. For example, genetics provides some insight into the likelihood of inheriting a medical condition such as a hemoglobinopathy like sickle cell anemia. Some conditions are the result of mutations involving a single gene, whereas other conditions may involve multiple genes and/or multiple chromosomes. Sickle cell disease is an example of an autosomal recessive disorder in which the offspring inherits a copy of the defective gene from each parent. Individuals with the sickle cell trait do not have the clinical manifestations of the disease but may pass the disease on to children if the other parent has the trait (or the disease) as well. Further information regarding inheritance of genes can be found in the study titled “Genetic Testing.”