Sickle cell anaemia Flashcards
What is the inheritance pattern of sickle cell anaemia?
Autosomal recessive
Briefly summarise what sickle cell anaemia is:
A production of abnormal haemoglobin results in vaso-occlusive crises
What is the genetic abnormality that causes SC anaemia?
Amino acid substitution in the gene coding for the Beta chain (Glutamine -> Valine) at position 6 which means HbS if formed instead of HbA.
They still have HbA2 and HbF.
What is the difference between homozygotes HbSS and heterozygotes HbAS?
Homozygotes - Sickle cell anaemia
Heterozygotes - Sickle cell trait. Causes no disability and protects from falciparum malaria.
Do heterozygotes get symptoms?
They can get sickling in hypoxia eg unpressurised aircraft, anaesthesia
What is the pathophysiology of how sickle cells form?
HbS polymerises when deoxygenated, causing RBC to deform, produce sickle cells.
These are fragile and haemolyse, and block small blood vessels.
What investigations would you do to confirm sickle cell anaemia?
Confirm haemolytic anaemia is present: - Low Hb - Raised reticulocytes - Raised bilirubin Blood film: - Sickle cells - Target cells Sickle solubility test: - Positive (detects HbS is present) Hb electrophoresis: - Confirms diagnosis and distinguishes between HbAS and HbSS
What is an aplastic crises?
Is treatment needed?
- Triggered by parvovirus
- Causes a sudden fall in Hb
- Usually self limiting <2wks, tranfusion may be needed
What will happen to the reticulocyte count in an aplastic crises?
Reduced due to bone marrow failure
What is a sequestration crises?
Sickling within organs such as the spleen or lungs causes pooling of blood, worsening the anaemia.
What is the treatment for a sequestration crises?
Urgent blood transfusion
What will happen to the reticulocyte count with a sequestration crises?
INCREASED
What can trigger a vaso-occlusive ‘painful’ crises?
Cold, dehydration, infection, hypoxia
How can a vaso-occlusive crises present?
- Mesenteric ischaemia
- Stroke, seizure
- Avascular necrosis of femoral head
- Priaprism
What is acute chest syndrome?
Vaso-occlusion crises in the pulmonary microvasculature, leading to infarction in the lung parenchyma
How can acute chest syndrome present?
- Dyspnoea
- Chest pain
- Pulmonary infiltrates on chest xray
- low pO2
How do you manage acute chest syndrome?
- Pain relief
- O2 therapy
- Antibiotics as infection may precipitate acute chest syndrome (cephalosporin + macrolide)
- Blood transfusion to improve oxygenation
- Consider bronchodilators
What is a haemolytic crises?
Fall in Hb due to increased rate of haemolysis
What complications occur with sickle cell anaemia?
- Splenic infarction so increased risk of infections
- Poor growth
- Chronic renal failure
- Gall stones
- Retinal disease
- Iron overload
- Lung damage -> hypoxia -> Fibrosis -> Pulmonary hypertension
What is the general management for sickle cell anaemia?
- Hydroxycarbamide (increases HbF)
- Hyposplenism -> Prophylactic antibiotics and imms
- Rescue outpatient antibiotics to prevent sepsis
- Bone marrow transplant (controversial)
How do you manage a sickle cell crises?
- Prompt generous analgesia (do they have a personalised analgesia plan?)
- Crossmatch blood - FBC, reticulocytes
- Temp? - septic screen (CXR, MSU, blood cultures)
- Rehydrate with IV fluids and O2
- Start antibiotics empirically if unwell
- Measure PCV, reticulocytes, liver and spleen size twice daily.
- Blood tranfusion
- Refer to haematology
How often do you give the pneumococcal vaccine?
Every 5 years
