July is Sickle Cell Awareness Month so we have chosen this disease for this week’s #TestingTuesday in order to give our followers a chance to learn something about sickle cell disease - a rare genetic blood disorder.
Sickle cell disease is the most common inherited blood disorder in the UK. There are 250,000 people who are carriers of the sickle cell gene and up to 13,500 who have sickle cell disease. Each year 350 new-born babies are diagnosed with sickle cell disease each year. In Britain it is mainly those of African or Caribbean descent who carry the sickle cell gene – at least 1 in 10 – 40 have the sickle cell trait and 1 in 60 – 200 have sickle cell disease.
What is sickle cell trait? Is it different from sickle cell disease?
In order for someone to inherit sickle cell disease, they must inherit two defective genes – one from each biological parent. It is possible to only inherit one defective gene from one biological parent. You would then be considered a carrier of sickle cell trait. Those with the sickle cell trait lead a relatively symptomless life – it would just be a good idea to have your partner tested, should you decide to have children.
Sickle cell diseases
The disorder affects the red blood cells which contain a special protein called haemoglobin (Hb for short). The function of haemoglobin is to carry oxygen from the lungs to all parts of the body.
People with sickle cell anaemia have sickle haemoglobin (HbS) which is different from the normal haemoglobin (HbA). When sickle haemoglobin gives up its oxygen to the tissues, it sticks together to form long rods inside the red blood cells making these cells rigid and sickle-shaped. Normal red blood cells can bend and flex easily.
Because of their shape, sickled red blood cells can't squeeze through small blood vessels as easily as the almost donut-shaped normal cells. This can lead to these small blood vessels getting blocked which then stops the oxygen from getting through to where it is needed. This in turn can lead to severe pain and damage to other parts of the body such as the spleen, kidney or bone marrow. Painful episodes are called ‘crises’ and they can be caused by dehydration, infection or a change in altitude.
There are three types of sickle cell crisis: aplastic, haemolytic, and painful.
• Aplastic – This type is due to infections, particularly parvoviruses, and results in a decrease in production of red blood cells. It may be self-limiting in 5-10 days
• Haemolytic – This anaemia is more severe, resulting in a sudden increase in the destruction of red blood cells. The bone marrow cannot produce cells fast enough to compensate for the loss, resulting in a critical decrease in haemoglobin and haematocrit. Transfusions are frequently needed to replace the red blood cells. In children, repeated crises could cause an enlarged spleen, which increases the risk of it rupturing
• Painful – This type is associated with severe pain due to the rigid sickle cells blocking the blood vessels, causing damage to cells and organs. It usually lasts 4-6 days, but may persist for weeks
There are also other different types of haemoglobin such as HbC and beta thalassaemia, that can combine with sickle haemoglobin to cause sickling disorders. When someone carries the gene for beta-thalassaemia they cannot make as much HbA as they should. If this is combined with the HbS gene then more of their total amount of haemoglobin is HbS and they can suffer from what is usually a milder form of sickle cell disorder than sickle cell anaemia.
How do I get tested for sickle cell disease?
A hemoglobin electrophoresis test measures the different types of hemoglobin in the bloodstream. Hemoglobin, the oxygen-carrying protein inside red blood cells, comes in many molecular forms, some normal and some abnormal. Normal hemoglobin carries and releases oxygen efficiently, while abnormal hemoglobin doesn't.
The most common types of normal hemoglobin are:
Hemoglobin F, the normal type found in fetuses and newborns. It's replaced by hemoglobin A soon after birth.
Hemoglobin A, the normal type most commonly found in healthy kids and adults.
Hemoglobin S, C, D, E, M, and hundreds of rarer kinds, the abnormal hemoglobin types.
If a person inherits the genes that cause production of too much of an abnormal type of hemoglobin, or not enough normal hemoglobin, it can lead to blood disorders, such as sickle cell disease. HbS is responsible for most types of sickle cell disease, a condition in which the red blood cells have a crescent or sickle shape that causes them to break down too quickly and clog small blood vessels.
If the screening test is negative, it means that the gene for sickle cell trait is not present. If the screening test is positive, then further haemoglobin testing must be performed to confirm whether one mutated gene or both are present. In unaffected individuals HbS is not present. In those who have sickle cell trait, 20% to 40% of the haemoglobin is HbS. In sickle cell disease, as much as 80% to 100% of the haemoglobin may be HbS. In general, individuals who have sickle cell trait do not have any significant symptoms and live a normal life. Those individuals who carry both abnormal genes have sickle cell disease. In this condition the person may not experience any symptoms under 'normal' conditions, but may experience episodes called 'sickling crises' brought on by, for example, infection or dehydration. During such episodes symptoms can include joint pain, abdominal pain, fever and seizures. In the long-term, sufferers may may experience haemolytic anaemia (breakdown of red blood cells), growth impairment, jaundice and increased risk of serious infections.
The full blood count is used as a broad screening test to check for such disorders as anemia. It is actually a panel of tests that examines different parts of the blood and includes the following:
- White blood cell (WBC)
- White blood cell differential looks at the types of white blood cells present
- Red blood cell (RBC) count is a count of the actual number of red blood cells per volume
- Hemoglobin measures the amount of oxygen-carrying protein in the blood
- Hematocrit measures the amount of space red blood cells take up in the blood
The reticulocyte count is used to help determine if the bone marrow is responding adequately to the body’s need for red blood cells (RBCs) and to help determine the cause of and classify different types of anaemia. The number of reticulocytes must be compared to the number of RBCs to calculate a percentage of reticulocytes And haemoglobin and/or haematocrit are also usually requested to help evaluate the severity of anaemia.
If you would like to know more about #TestingTuesday, or if you are an interested patient group, please contact Gemma Scotcher on email@example.com or follow us @bivda
More information about sickle cell diseases and sickle cell testing can be found at:
Lab Tests Online: http://www.labtestsonline.org.uk/understanding/conditions/sickle
Sickle Cell Society http://www.sicklecellsociety.org
If there is a link which should be added to this list, please let us know.