The Test Sample
What is being tested?
A hemoglobinopathy is an inherited blood disorder in which an individual has an abnormal form of hemoglobin (variant) or decreased production of hemoglobin (thalassemia). A hemoglobinopathy evaluation is a group of tests that identifies abnormal forms of or suggests problems with production of hemoglobin in order to screen for and/or diagnose a hemoglobin disorder.
Hemoglobin (Hb) is the iron-containing protein found in all red blood cells (RBCs) that binds to oxygen in the lungs and allows RBCs to carry the oxygen throughout the body, delivering it to the body's cells and tissues. Hemoglobin consists of one portion called heme, which is the molecule with iron at the center, and another portion made up of four globin (protein) chains. The globin chains, depending on their structure, have different designations: alpha, beta, gamma, and delta. The types of globin chains that are present are important in the function of hemoglobin and its ability to transport oxygen.
Normal hemoglobin types include:
- Hemoglobin A: makes up about 95%-98% of Hb found in adults; it contains two alpha and two beta protein chains.
- Hemoglobin A2: makes up about 2%-3% of Hb in adults; it has two alpha and two delta protein chains.
- Hemoglobin F (fetal hemoglobin): makes up to 1%-2% of Hb found in adults; it has two alpha and two gamma protein chains. This is the primary hemoglobin produced by the fetus during pregnancy; its production usually falls shortly after birth and reaches adult levels by 1-2 years.
Hemoglobinopathies occur when changes (mutations) in the genes that code for the globin chains cause alterations in the proteins. These genetic changes may result in a reduced production of one of the normal globin chains or in the production of structurally altered globin chains. Genetic mutations may affect the structure of the hemoglobin, its behavior, its production rate, and/or its stability. The presence of abnormal hemoglobin within RBCs can alter the appearance (size and shape) and function of the red blood cells.
Red blood cells containing abnormal hemoglobin (hemoglobin variants) may not carry oxygen efficiently and may be broken down by the body sooner than usual (a shortened survival), resulting in hemolytic anemia. Some of the most common hemoglobin variants include hemoglobin S, the primary hemoglobin in people with sickle cell disease that causes the RBC to become misshapen (sickle), decreasing the cell's survival; hemoglobin C, which can cause a minor amount of hemolytic anemia; and hemoglobin E, which may cause no symptoms or generally mild symptoms.
Thalassemia is a condition in which a gene mutation results in reduced production of one of the globin chains. This can upset the balance of alpha to beta chains, causing abnormal hemoglobin to form (alpha thalassemia) or causing an increase of minor hemoglobin components, such as Hb A2 or Hb F (beta thalassemia).
Many other less common hemoglobin variants exist. Some are silent – causing no signs or symptoms – while others affect the function and/or stability of the hemoglobin molecule. An investigation of a hemoglobin disorder typically involves tests that determine the types and amounts of hemoglobin present in a person's sample of blood. Some examples include:
- Hemoglobin solubility test: used to test specifically for hemoglobin S, the main hemoglobin in sickle cell disease
- Hemoglobin electrophoresis (Hb ELP)
- Hemoglobin isoelectric focusing ( Hb IEF)
- Hemoglobin by high performance liquid chromatography (HPLC)
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.