Sickle-cell anaemia Flashcards
(33 cards)
What is sickle-cell anaemia?
Sickle-cell anaemia is an autosomal recessive condition that results from the synthesis of an abnormal haemoglobin chain termed HbS.
In which population is sickle-cell anaemia more common?
It is more common in people of African descent as the heterozygous condition offers some protection against malaria.
What percentage of UK Afro-Caribbean’s are carriers of HbS?
Around 10% of UK Afro-Caribbean’s are carriers of HbS (i.e. heterozygous).
When do symptoms develop in homozygotes?
Symptoms in homozygotes don’t tend to develop until 4-6 months when the abnormal HbSS molecules take over from fetal haemoglobin.
What are the types of haemoglobin associated with sickle-cell disease?
Normal haemoglobin: HbAA, sickle cell trait: HbAS, homozygous sickle cell disease: HbSS, and a milder form: HbSC.
What amino acid substitution occurs in sickle-cell anaemia?
The polar amino acid glutamate is substituted by non-polar valine in each of the two beta chains (codon 6).
What effect does the substitution have on deoxy-Hb?
This substitution decreases the water solubility of deoxy-Hb.
What happens to HbS molecules in the deoxygenated state?
In the deoxygenated state, the HbS molecules polymerise and cause RBCs to sickle.
At what pO2 do HbAS patients sickle?
HbAS patients sickle at pO2 2.5 - 4 kPa.
At what pO2 do HbSS patients sickle?
HbSS patients sickle at pO2 5 - 6 kPa.
What are the consequences of sickle cells?
Sickle cells are fragile and haemolyse; they block small blood vessels and cause infarction.
How is sickle cell disease definitively diagnosed?
The definitive diagnosis of sickle cell disease is by haemoglobin electrophoresis.
What is the first step in managing a sickle-cell crisis?
Analgesia e.g. opiates
What is a key component of crisis management for sickle-cell anaemia?
Rehydrate
What should be administered to sickle-cell patients during a crisis?
Oxygen
When should antibiotics be considered in sickle-cell crisis management?
If there is evidence of infection
What type of transfusion may be necessary for neurological complications in sickle-cell patients?
Exchange transfusion
What medication is used for longer-term management of sickle-cell anaemia?
Hydroxyurea
What does hydroxyurea do in sickle-cell patients?
Increases the HbF levels and is used in prophylactic management to prevent painful episodes
How often should sickle cell patients receive the pneumococcal polysaccharide vaccine?
Every 5 years
What characterizes sickle cell anaemia?
Sickle cell anaemia is characterised by periods of good health with intervening crises.
What are the types of sickle cell crises?
The types of crises are thrombotic, acute chest syndrome, anaemic, aplastic, sequestration, and infection.
What are thrombotic crises also known as?
Thrombotic crises are also known as painful crises or vaso-occlusive crises.
What precipitates thrombotic crises?
Thrombotic crises are precipitated by infection, dehydration, and deoxygenation (e.g. high altitude).
