11. Sickle Cell Anaemia Flashcards
What does it mean if someones RBCs are crescent shaped?
This is another word for sickle shaped, indicating sickle cell anaemia
What are the two main components in red blood cells?
- Heme, containing the iron
- Globin chains, which are proteins
What are the types of globin chains?
- Alpha
- Beta
- Delta
- Gamma
What are the normal / most common 3 haemoglobin variants
- Haemoglobin F (this is featal haemoglobin)
- Haemoglobin A (95%-98% of adults have this)
- Haemoglobin A2 (2-3% of adult population have this)
What is the composition of Haemoglobin F?
It consists of both;
- 2 alpha chains
- 2 gamma chains
What is the composition of Haemoglobin A?
It consists of both;
- 2 alpha chains
- 2 beta chains
What is the composition of Haemoglobin A2?
It consists of both;
- 2 alpha chains
- 2 delta chains
What is Haemoglobin S?
This is one of several hundred abnormal forms of haemoglobin.
Specifically, it is known as sickle cell disease if you are homozygous for it.
What are the globin chains like in someone with sickle cell disease?
- 2 abnormal beta chains (coded from chromosome 11)
- 2 normal alpha chains
When do the RBCs become sickle shaped in sickle cell anaemia?
When they have decreased amounts of oxygen (ex. during exercise, infection etc.)
What is sickle cell trait?
This is when an individual only has 1 globin chain that is abnormal. Therefore it would be
- 1 abnormal beta chain
- 1 normal beta chain
- 2 normal alpha chains
Do those with sickle cell trait have symptoms?
They are normally asymptomatic.
However, if sickle-cell trait is combined with another haemoglobin mutation (ex. Hb C or thalassaemia, then they can have significant symptoms
What happens to the sickle shaped RBCs as they travel through the body?
Normal shape when oxygenated.
Once they become less oxygenated, they turn into sickle shapes. This can block capillaries, cause pain, aand result in decreased oxygen delivery.
As they are abnormal, they are filtered out by the reticulo-endothelial system early, meaning there is decreased red cell survival.
Are individuals with haemoglobin C symptomatic?
If they have only 1 mutated gene, then typically they are asymptomatic
If they have 2 mutated gene copies, then typically they are symptomatic
Similarly, if they have 1 abnormal gene, then have 1 abnormal gene for another condition (ex. sickle cell, thalassaemia etc.) then they are normally symptomatic.
What is haaemoglobin SC disease? What symptoms does it cause?
This is when you have 1 copy of Hb S and one copy of Hb C.
On their own, they would not produce symptoms. But as they both are abnormal, together, it causes symptoms. They have
- Mild haemolytic anaemia
- Moderate enlargement of the spleen
Among which group of the population is sickle cell disease most common? Why?
It is most common in patients from areas typically affected by Malaria (Africa, India, Middle East, Carribean).
This is because having 1 copy of Hb S (ie. having sickle-cell trait) has been proven to reduce the severity of malaria. Therefore there is a selective advantage to have sickle-cell trait, so through natural evolution, those with 1 copy have survived better, leading to a higher proportion of the population in these areas having the gene.
When do you get tested for sickle cell disease?
- Pregnant women at risk of carrying the gene are offered testing
- Newborns are tested as part of the heel prick test at 5 days of age
What are the key diagnostic features in someone with sickle cell anaemia?
- Anaemia symptoms (fatigue, weakness)
- Parent diagnosed with sickle cell disease / sickle cell trait / other sickle cell condition such as Hb SC
- Persistent pain in skeleton, chest or abdomen
- Dactylitis
What is Dactylitis? Why does it happen in sickle-cell disease?
Also reffered to as Hand-foot syndrome, it is the swelling of the dorsa of the hands and feet.
It occurs due to blood vessels becoming blocked due to the sickle cells, and therefore ther is accumulation of blood in the peripheral limbs.
What are the complications of sickle-cell anaemia?
- Anaemia
- Increased risk of infection
- Stroke
- Avascular necrosis in large joints such as the hip
- Pulmonary hypertension
- Priapism
- Chronic kidney disease
- Sickle cell crises
- Acute chest syndrome
What is priapism?
Painful and persistent penile erection
What is the general management of sickle cell anaemia
Hint; general, pharmacological and other
General
- Avoid dehydration and other triggers of crisis
- Ensure vaccines are up to date
Pharmacological
- Antibiotic prophylaxis to protect against infection with penicillin V (phenoxymethypenicillin)
- Hydroxycarbamide can be used to stimulate production of fetal haemoglobin (HbF). Fetal haemoglobin does not lead to sickling of red blood cells. This has a protective effect against sickle cell crises and acute chest syndrome.
Infusions / Transplants
- Blood transusions for severe anaemia
- Bone marrow transplant can be curative
What medication can be given to those with sickle cell anaemia? How does it work?
Hydroxycarbamide can be used. It stimulates production of fetal haemoglobin, which does not lead to the sickening shape
What is meant by the term sickle cell crisis?
It is an umberella term for a spectrum of acute crises related to the condition ranging in severity from mild to life threatening
Examples of crises include
- Vaso-occlusive crisis
- Splenic sequestration crisis
- Aplastic crisis
- Acute chest syndrome
