Sickle cell disease Flashcards
what is a haemoglobinopathy and what are the two types?
A defect in the haemoglobin molecule and they are divided into:
Haemoglobin variants: 4 chains are present but structurally there is something wrong with the chains. Sickle cell is the main example.
Thalassaemias- There is a problem with the production of the haemoglobin leading to structurally normal haemoglobin with decreased or absent production.
what are the chains and genes in normal haemoglobin?
Normal haemoglobin (HbA) consists of 2 alpha and 2 beta chains. This is made from 2 alpha and 4 beta globin genes.
If you inherit normal alpha and beta globin genes what is your haemoglobin made up of?
94-98% HbA (normal),
2-4% HbA2,
0.8-2% HbF
0% HbS (sickle)
What are the main categories of sickle cell?
- Homozygous sickle cell anaemia: Inherit the abnormal sickle gene from both parents so phenotype is HbSS.
- Heterozygous mutation (sickle cell disease):
Inherit two different recessive alleles one of the sickle gene and the other another haemoglobin variant of the beta globin gene. - Sickle-thalassaemia:
Inherit a sickle gene and a thalassaemia gene causing abnormal production and structure. Severity depends on which thalassaemia gene is inherited.
Sickle cell trait- inherits a single sickle copy and rarely causes symptoms- a carrier.
what is the inheritance pattern of sickle cell?
A.Recessive
what is the mutation in the beta globin gene causing sickle cell?
A point mutation on chromosome 11 causing valine to be swapped to glutamic acid
How is sickle cell diagnosed?
New born heel test at day 5.
Antenatal screening by week 10 in high risk couples
Identification of the sickle erythrocytes: haemoglobin electrophoresis, DNA sequencing.
what blood results are shown in sickle cell?
Raised reticulocytes, low haptoglobin and raised billirubin due to increased haemolysis
Blood film microscopy: sickle shaped erythrocytes and Howell- Jolly bodies (HJB only if hyposplenic).
what are examples of acute crises?
- Vaso-occlusion
- Acute chest syndrome
- Aplastic crisis
- Hand foot syndrome
what is vaso-occlusion?
This is an acute pain crisis.
The cells sickle causing blockage of multiple vessels and organs.
what are symptoms and findings in an acute chest crisis?
Clinical features:
- SOB
- fever
- resp symptoms
Findings:
- new pulmonary infiltrate on CXR
- hypoxia
what is the main management for acute chest syndrome?
Urgent exchange transfusion
what is aplastic crisis?
Due to infection (mainly Parvovirus B19) there is a sudden hault to the production of RBC’s causing a sudden drop in Hb.
What is hand-foot syndrome?
A crisis causing dactylitis which normally lasts for around a week.
what are complications/features of sickle cell?
Jaundice Dactylitis Chronic organ damage retinopathy pulmonary HTN priapism stroke avascular necrosis sequestration sepsis increased susceptibility to encapsulated bacteria
what factors can trigger a vaso-occlusive episode?
Hypoxia
dehydration
infection
cold exposure stress
what investigations should be done for an acute painful presentation?
Bloods and ABG if chest signs
CXR
plain XR of line bones
ECG
what are the categories of management for sickle cell?
Prevention
Acute complications
Chronic complications
what is the ongoing management for sickle cell?
Long term Abx especially penicillin
Folic acid 5mg daily
Immunisations (seasonal influenza, 5 yr pneumococcal, meningitis and hep B)
Hydroxyurea (increases the amount of foetal Hb and helps RBC’s last longer than 20 days)
what are the indications for hydroxyurea to be started?
More than 3 acute painful episodes needing admission
Acute chest syndrome needing transfusion/ high dependency unit
Previous stroke
what is the management of an acute painful episodes?
ABCDE Observations Check sickle cell care plan Fluids Oxygen Analgesia Abx Referral
what is the management of acute chest syndrome?
ABCDE Observations Oxygen Invasive spirometry (goal to prevent atelectasis) Analgesia Broad spec Abx as can't rule out bacterial pneumonia Blood transfusion Fluids
what bacteria are sickle cell patients more at risk of?
Encapsulated such as H.influenzae and Strep pneumoniae due to hyposplenism
what is done for stroke prevention in younger patients with sickle cell?
Annual transcranial doppler ultrasounds to assess risk. If high risk they will be offered regular transfusions
what are key questions to ask a patient who is presenting with an acute presentation of known sickle cell disease?
What is their diagnosis?
Do they have their care plan?
What is their preventative strategy ie hydroxyurea/exchange programme?
Last sickle percentage and haemoglobin baseline?
what findings does an aplastic crisis find?
Sudden anaemia
low reticulocyte count
