What is the purpose of this test?
Order this Hemoglobin (Hb) Solubility Blood Test to detect the presence of abnormal hemoglobin S (Hb S) and help screen for sickle cell anemia. In addition, this test may help diagnose other hemoglobin disorders such as hemoglobin C disease, hemoglobin S-C disease, and thalassemia.
The Hemoglobin Solubility Test detects Hb S, which is present in individuals with sickle cell anemia or sickle cell trait. "Solubility" refers to how well a substance dissolves in a liquid. In this case, the substance is the hemoglobin molecule, the major protein in RBCs, and the liquid is blood plasma.
Usually, for individuals without sickle cell disease or sickle cell trait, the most common hemoglobin is Hb A, which dissolves quickly in the blood. As a result, the plasma remains clear but will take on a red color. However, the hemoglobin from an individual with sickle cell disease is Hb S. Hb S does not dissolve easily in blood plasma. Instead, the plasma will become cloudy because the Hb S forms tiny crystals. Therefore, a person with the sickle trait will have Hb A and Hb S. They will have some clouding but less than the full-blown sickle cell disease.
A more sophisticated test, such as the Hemoglobinopathy Evaluation Blood Test, is ordered if a person has a positive sickle cell solubility. The Hemoglobinopathy Evaluation Blood Test uses the hemoglobin electrophoresis methodology. It is usually performed to confirm the diagnosis and rule out other conditions that may cause an abnormal sickle cell solubility test.
What is hemoglobin (Hb)?
Hemoglobin (Hb) is a protein found in the red blood cells that transfers oxygen from the lungs to the rest of the body. There are several different types of hemoglobin, such as:
- Hb A - comprises approximately 95%-98% of Hb found in adults. This hemoglobin contains two alpha and two beta protein chains.
- Hb A2 - accounts for about 2%-3% of Hb in adults; it is characterized by two alpha and two delta protein chains.
- Hb F - (Fetal hemoglobin) makes up 1%-2% of Hb found in adults; it contains two alpha and two gamma protein chains. Additionally, this is the primary hemoglobin produced by the fetus during pregnancy. The production of Hb F usually drops right after birth and reaches adult levels within 1-2 years.
- Hb S - the primary hemoglobin in individuals with sickle cell disease, which causes the RBC to become misshapen (sickle-shaped), decreasing the cell's survival
- Hb C - is the hemoglobin that can cause minor hemolytic anemia.
- Hb E -the only hemoglobin which may cause no symptoms or generally mild symptoms and is primarily found in individuals of Southeast Asian descent.
What causes sickle cell anemia?
Unfortunately, some individuals inherit hemoglobin diseases, also known as hemoglobinopathy, in which there is abnormal production or structure of the hemoglobin protein. For example, an abnormal amount of hemoglobin (Hb) S is found in individuals with sickle cell anemia. Sickle cell anemia is an inherited disease that causes the body to create inflexible, "sickle" shaped red blood cells. Red blood cells should be flexible to flow easily through blood vessels; however, sickle cells can get stuck in the blood vessels.
When should I order a Hemoglobin (Hb) Solubility Blood Test?
Individuals may order this test if they have experienced symptoms related to sickle cell anemia. Patients with abnormal levels of Hb S or sickle cell anemia may experience symptoms such as:
- Severe or chronic pain
- Anemia
- Shortness of breath
- Enlarged spleen
- Frequently recurring infections
- Coughing
- Chest pain
- Fever
