Sickle cell Flashcards Preview

Module 103, Theme 2: Formation, composition, function and disorders of the blood. > Sickle cell > Flashcards

Flashcards in Sickle cell Deck (22)
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1

Genetics of SCD

Point mutation in beta-globin gene- valine (no charge) substituted for glutamic acid (negatively charged) at the 6th amino acid.

This mutation forms HbS, when forms parallel aggregates when deoxygenated- forms 'sickly' looking rbc.

This mutation is inherited in an autosomal recessive fashion.

2

Physiological effects of sickled red cells

The cells have an increased mechanical fragility, thus shorter lifespan: 6-10 days.

Rigid sickle cells make the blood more viscous, which can occlude small blood vessels.

Sickle cells also stick to the endothelium.

3

Epidemiology of SCD

The disease is distributed mainly across the Afro-Caribbean population.

Also mainly present in: India, Middle East, North Africa

Distribution of the condition correlates with incidence of Plasmodium falciparum- the sickle cell carriers have a selective advantage against the infection.

4

Oxygen dissociation curve for SCD

Due to low Hb, this is compensated by an increase in 2,3-DPG.

This stabilises R state further.

The dissociation curve shifts to the right, having even less affinity to O2, thus oxyhaemoglobin releases its O2 to tissues at higher PO2 levels.

5

Clinical features of SCD

Presents usually during infancy.

Anaemia

Jaundiced

Dactylitis

Splenic sequestration in children

Vaso-occlusive crisis

Pneumococcal septicaemia.

6

Dactylitis

Inflammation of of an entire finger or toes.

A clinical presentation of sickle cell anaemia.

If the epiphyseal plate is damaged, it can shorten the digit.

7

Chest syndrome

A clinical feature of sickle cell anaemia:

Dyspnoea
Pleuritic chest pain
Patchy shadowing on the CXR
Progressive hypoxia and fever.

8

Brain syndrome

A clinical feature of sickle cell which presents as stroke.

9

Aplastic crisis

A clinical feature of sickle cell.

It is a temporary cessation of RBC production.

When a SC person is infected with a parvovirus, this crisis occurs.

This causes severe anaemia.

10

Blood film for SCD

Sickle cells- spindle/boat shape.

Polychromasia: an abnormally high number of immature rbc (usually reticulocytes).

Howell-Jolly bodies: red blood cells with nuclear remnants- they are being pushed out of the cells prematurely

11

Sickle solubility test

Diagnosis for SCD:

Sodium dithionite is added to blood and will make RBC lyse and release Hb.

RBC with HbA will dissolve easily and form clear, red plasma.

RBC with HbS, will not dissolve as easily, The plasma will be cloudy due to the formation of crystals.

RBC with HbS and HbA (sickle cell trait), will have some clouding but not full blown like HbS.

12

Haemoglobin analysis

Diagnostic test used for SCD:

Hb electrophoresis-

Different Hb types have different charges. Electrophoresis separates the different Hb according to their charge.

Hb HPLC:
High performance liquid chromatography.

It analyses the types of Hb according to chemical properties- like gas chromatography.

13

Management of SCD

Antenatal screening

Prophylaxis against infections: penicillin, vaccinates

Prevention of crises.

14

Prevention of stroke in SCD

Transcranial doppler

If the blood flow is >200 cm/sec, this shows that the risk of stroke is significantly increased.

Stroke risk is reduced by exchange transfusion or hydroxyurea.

15

Management of crisis in SCD

Exclude any underlying infection.

Administer IV fluids.

O2 and analgesia

Antibiotics

FBC and reticulocyte count.

16

Analgesics given during the management of crisis in SCD

NSAID's

Opiates

Pethidine is avoided for seizures and addiction.

17

Exchange transfusion

A blood transfusion where the patient's blood (SCD) is replaced with other blood.

Blood must match: ABO, Rhesus, Kell and sickle negative.

This aims to reduce HbSS to <20%.

18

Indications for exchange transfusion for SCD

Chest syndrome

Stroke

Major surgery

Recurrent severe crisis

Priapism.

19

Complications with SCD

Proliferative retinopathy

Avascular necrosis of femoral/ humeral heads

Bone infarcts

Osteomyelitis

Papillary necrosis/ renal failure- necrosis of renal papilla

Leg ulcers

Gallstones.

20

Proliferative retinopathy

Complication that can arise in individuals with SCD-

New blood vessels grow on the surface of the retina and can bleed.

21

Hydroxyurea

Fairly recent treatment for SCD

Reduces frequency of crises, chest syndromes and transfusions.

This increases HbF production

Decreases differential white cell count and platelets.

Causes a reduced expression of adhesion molecules in RBCs.

Increases NO production.

22

Allogeneic stem cell transplantation

A potentially curative method for SCD

Usually only administered to patients below 16.

80-85% are cured from this treatment.

Risks:
Infertility
5-10% risk of chronic graft vs host disease.