Hb electrophoresis

A haemoglobinopathy is an inherited blood disorder in which an individual has an abnormal form of haemoglobin (variant) or decreased production of haemoglobin (thalassaemia). A haemoglobinopathy evaluation is a group of tests that identifies abnormal forms of or suggests problems with production of haemoglobin in order to screen for and/or diagnose a haemoglobin disorder.

Haemoglobin (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. Haemoglobin consists of one portion called haeme, which is the molecule with iron at the centre, 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 haemoglobin and its ability to transport oxygen.

Normal haemoglobin types include:

• Haemoglobin A: makes up about 95%-98% of Hb found in adults; it contains two alpha and two beta protein chains.
• Haemoglobin A2: makes up about 2%-3% of Hb in adults; it has two alpha and two delta protein chains.
• Haemoglobin F (foetal haemoglobin): makes up to 1%-2% of Hb found in adults; it has two alpha and two gamma protein chains. This is the primary haemoglobin produced by the foetus during pregnancy; its production usually falls shortly after birth and reaches adult levels by 1-2 years.

Haemoglobinopathies 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 haemoglobin, its behaviour, its production rate, and/or its stability. The presence of abnormal haemoglobin within RBCs can alter the appearance (size and shape) and function of the red blood cells.

Red blood cells containing abnormal haemoglobin (haemoglobin variants) may not carry oxygen efficiently and may be broken down by the body sooner than usual (a shortened survival), resulting in haemolytic anemia. Some of the most common haemoglobin variants include haemoglobin S, the primary haemoglobin in people with sickle cell disease that causes the RBC to become misshapen (sickle), decreasing the cell's survival; haemoglobin C, which can cause a minor amount of haemolytic anaemia; and haemoglobin E, which may cause no symptoms or generally mild symptoms.

Thalassaemia 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 haemoglobin to form (alpha thalassaemia) or causing an increase of minor haemoglobin components, such as Hb A2 or Hb F (beta thalassaemia).

Many other less common haemoglobin variants exist. Some are silent – causing no signs or symptoms – while others affect the function and/or stability of the haemoglobin molecule. An investigation of a haemoglobin disorder typically involves tests that determine the types and amounts of haemoglobin present in a person's sample of blood. Some examples include:

• Haemoglobin solubility test: used to test specifically for haemoglobin S, the main haemoglobin in sickle cell disease
• Haemoglobin electrophoresis (Hb ELP)
• Haemoglobin isoelectric focusing ( Hb IEF)
• Haemoglobin by high performance liquid chromatography (HPLC)

Information from these tests, along with results from routine tests such as a full blood count (FBC) and blood film, aid in establishing a diagnosis.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.