Haemoglobinopathy Evaluation

A haemoglobinopathy evaluation is used to detect abnormal forms and/or relative amounts of haemoglobin, the protein found in all red blood cells that transports oxygen. Testing may be used for:

• Screening
  • All newborns are screened for certain haemoglobin variants.
  • Prenatal screening is often performed on high-risk parents with an ethnic background associated with a higher prevalence of haemoglobin abnormality and those with affected family members. Screening may also be done in conjunction with genetic counselling prior to pregnancy to determine whether the parents are carriers.
  • To identify variants in asymptomatic parents who have an affected child

• Diagnosis
  • To detect and/or identify haemoglobinopathy (haemoglobin abnormality or thalassaemia) in those with symptoms of unexplained anaemia or abnormal results on a full blood count (FBC)

Several different laboratory methods are available to evaluate the types of haemoglobin that a person has. Some of these 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)
• Capillary electrophoresis

These methods evaluate the different types of haemoglobin based on the physical and chemical properties of the different haemoglobin molecules. Most of the common haemoglobin variants or thalassaemias can be identified using one of these tests or a combination. The relative amounts of any variant haemoglobin detected can aid in a diagnosis. However, a single test is usually not sufficient to establish a diagnosis of haemoglobinopathy. Rather, the results of several different tests are considered. Examples of other laboratory tests that may be performed include:

• FBC
• Blood film
• Reticulocyte count
• Iron studies such as serum iron, TIBC, transferrin
• Genetic testing: may be used to detect mutations in the genes that code for the protein chains (alpha and beta globulin) that comprise haemoglobin. This is not a routine test but can be used to confirm whether a person has a mutated gene and whether there is one or two mutated copies (heterozygous or homozygous).

Testing for haemoglobinopathies is required as part the national newborn screening program. In addition, it is often used for prenatal screening when a parent is at high risk or when parents have a child who has a haemoglobinopathy. An evaluation is usually ordered when results of a full blood count (FBC) and/or blood film indicate that a person may have an abnormal form of haemoglobin.

It may be requested when a doctor suspects that a person's signs and symptoms are the result of abnormal haemoglobin production. Abnormal forms of haemoglobin often lead to haemolytic anaemia, resulting in signs and symptoms such as:

• Weakness, fatigue
• Lack of energy
• Jaundice
• Pale skin

Some severe forms of haemoglobinopathies (e.g., sickle cell disease) may result in serious signs and symptoms, such as episodes of severe pain, shortness of breath, enlarged spleen, and growth problems in children.

Care must be taken when interpreting the results of a haemoglobinopathy evaluation. Typically, the laboratory report includes an interpretation by a haematologist.

Results of the evaluation usually report the types of haemoglobin present and the relative amounts. For adults, percentages of normal haemoglobins include:

• Haemoglobin A1(HB A1): about 95%-98%
• Haemoglobin A2 (Hb A2): about 2%-3%
• Haemoglobin F (Hb F): 2% or less

Testing may help diagnose a condition that causes the production of structurally altered haemoglobin (variant) or a condition called thalassaemia, 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).

Some of the most common abnormal forms of haemoglobin that may be detected and measured with this testing include:

• Haemoglobin S (Hb S): this is the primary haemoglobin in people with sickle cell disease. Most people affected are of African or African-Caribbean origin. It is estimated that there are between 12,500-15,000 people with sickle cell disease in the UK according to the NICE guidance.

  Individuals with sickle cell disease (two copies of the abnormal gene) have a high percentage of Hb S. People with sickle cell trait have a moderate amount of Hb S (about 40%) but still have the normal form of Hb A (about 60%). Hb S causes the red blood cell to become misshapen (sickle) when exposed to a low level of oxygen (such as might happen when someone exercises or has infection in the lungs). Sickled red blood cells can block small blood vessels, causing pain, impaired circulation, and decreased oxygen delivery to tissues and cells, and decrease the cell's survival. High amounts of haemoglobin A or F can keep enough oxygen in the red blood cells to prevent sickling from occurring.

• Haemoglobin C (Hb C): about 2-3% of people of African descent have haemoglobin C trait (one copy of the gene for Hb C). Haemoglobin C disease (seen in those with two copies of the gene) is rare and relatively mild. It usually causes a minor amount of haemolytic anaemia and a mild to moderate enlargement of the spleen.
• Haemoglobin E (Hb E): this is one of the most common beta chain haemoglobin variants in the world. It is very prevalent in individuals of Southeast Asian descent. People who are homozygous for Hb E generally have a mild haemolytic anaemia, microcytic red blood cells, and a mild enlargement of the spleen. A single copy of the haemoglobin E gene does not cause symptoms unless it is combined with another mutation (e.g., a mutation causing beta thalassaemia).

Some less common forms include:

• Haemoglobin F (Hb F): this is the primary haemoglobin produced by a developing foetus. Normally, production of Hb F drops significantly after birth and decreases to adult levels by 1-2 years of age. Hb F may be elevated in several disorders, such as beta thalassaemia and sickle cell anaemia.
• Haemoglobin H (Hb H): occurs in some cases of alpha thalassaemia. It is composed of four beta globin chains and is produced due to a severe shortage of alpha chains. Although each of the beta globin chains is normal, the four beta chains do not function normally.
• Haemoglobin Barts: this type develops in foetuses with alpha thalassaemia. It is formed of four gamma protein chains when there is a shortage of alpha chains, in a manner similar to the formation of Hb H. Hb Barts disappears shortly after birth due to dwindling gamma chain production.

Other types that may be identified include:

• Haemoglobin D
• Haemoglobin G
• Haemoglobin J
• Haemoglobin M
• Haemoglobin Constant Spring

A person can also inherit two different abnormal genes, one from each parent. This is known as being compound heterozygous or doubly heterozygous. Several different clinically significant combinations include haemoglobin SC disease, sickle cell – haemoglobin D disease, haemoglobin E – beta thalassaemia, and haemoglobin S – beta thalassaemia. For more on these, see the articles on Haemoglobin Abnormalities and Thalassaemia.

Some examples of results that may be seen with a haemoglobinopathy evaluation are listed in the following table.

Blood transfusions can interfere with haemoglobinopathy evaluation. A patient should wait several months after a transfusion before having this testing done. However, in people with sickle cell disease, the testing may be performed after a transfusion to determine if enough normal haemoglobin has been given to reduce the risk of damage from sickling of red blood cells.

Newborn screening helps to identify potentially treatable or manageable congenital disorders within days of birth. Potentially life-threatening health problems and serious lifelong disabilities can be avoided or minimised if a condition is quickly identified and treated. Also, since newborn screening programs have mandated testing for haemoglobin variants, they have uncovered thousands of children who are carriers. (This is due to new technology, not to an increased prevalence of the gene mutations.) Information on carrier status may be important in their future if and when they begin to plan a family.