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22nd July 2024
Sickle cell anaemia (SCA)
Overview of sickle cell anaemia
SCA is an autosomal recessive disorder affecting the Hb beta chain, causing HbS to be produced rather than HbA. It is most commonly seen in people of African ethnicity or descent. Sickle trait (HbAS) is protective against malaria.
In the UK, screening is available for pregnant women in high-risk groups, as well as neonatal screening. Children usually only become symptomatic after around 4 months, when HbS production takes over from foetal Hb (HbF). When exposed to reduced oxygen levels HbS deforms and forms sickle cells, which have poorer flow through vessels and can cause occlusion and sickle crises.
Investigations may show chronic haemolysis, anaemia, raised reticulocytes and bilirubin. The blood film shows sickle cells, nucleated RBCs and Howell-Jolly bodies (indicate hyposplenism). A sickle solubility test will be positive; however, electrophoresis is required to confirm the diagnosis and differentiate between HbSS and HbAS.
Long-term complications include anaemia, iron overload (secondary to transfusions), pigment gallstones, avascular necrosis, chronic kidney disease, pulmonary hypertension, hyposplenism, retinopathy and impaired growth.
Image Source: Wikimedia Commons (2011). Stomach blood supply, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/7/70/Sickle_Cell_Blood_Smear.JPG (Accessed: 16 January 2024)
Management of chronic sickle cell anaemia
Long-term management of sickle cell disease includes hydroxyurea to reduce HbS levels and increase HbF, prophylactic antibiotics (usually started in childhood), and vaccinations (pneumococcal and influenza) because of functional asplenism (due to repeated splenic infarction) that occurs whilst patients are young and increases the risk of severe infections from encapsulated bacteria.
Management of sickle cell crises
There are multiple acute manifestations of sickle cell anaemia. In general, these crises occur when HbS RBCs deform due to hypoxia, acidosis, dehydration, hypothermia or infection. This produces sickle-shaped cells, which can occlude vessels and are more prone to haemolysis. Patients are often well outside of crises.
A general approach to a patient with sickle cell disease presenting acutely to hospital will aim to identify any potential triggers or early signs of a sickle cell crisis and reduce the risk of patients developing a crisis:
- Supportive measures: adequate hydration, target sats >94%, keep warm
- Send a group and save and consider transfusion if the patient is anaemic below their baseline
- Check blood tests for signs of increased haemolysis
- Consider sending a HbS%
- Adequate analgesia
- Screen for infection and have a low threshold to perform a septic screen and start empirical antibiotics
Key clinical facts about specific types of sickle cell crises are as follows:
| Acute chest crisis | Episodes can occur with no specific trigger, however they are commonly triggered by infection, vaso-occlusive pain, fat embolism and asthma exacerbations.
It presents with chest pain, shortness of breath, fever, cough and wheeze, and can lead to multiorgan failure if not treated rapidly. Pulmonary infiltrates on chest X-ray are classical but initially may not be present. Acute management includes analgesia, oxygen, incentive spirometry to prevent further atelectasis, IV antibiotics (typically cefotaxime and azithromycin), RBC transfusion or exchange transfusion to reduce HbS% to <30, and possible early escalation for consideration of non-invasive (NIV) or mechanical ventilation. |
| Vaso-occlusive (VOC) or painful crisis | Microvascular occlusion often triggered by cold, dehydration, hypoxia or infection. Generally affects bones containing marrow, but other sites include mesenteric ischaemia, central nervous system (CNS) (strokes, cognitive impairment or seizures), avascular necrosis of the femoral head, leg ulcers and priapism (urological aspiration and irrigation may be required).
It is important to use the patient’s and their relative’s reports to assess pain. Analgesia should be administered within 30 minutes, and patients often have a personalised treatment plan, however IV morphine can be used if not. Reassessment following this is important as patients may need additional doses. Adequate hydration helps to improve symptoms, and exchange transfusion can be used to treat neurological complications, including an acute stroke, due to a VOC. |
| Aplastic crisis | Bone marrow suppression due to parvovirus B19 infection causing reduction in RBCs and reticulocytes. This is self limiting and usually resolves within 14 days, but supportive RBC transfusion may be needed. |
| Sequestration crisis | Pooling of blood, often in the spleen or liver, which worsens anaemia and can cause hypovolaemic shock. This often occurs in children whose spleens have not yet infarcted and become fibrotic. Viral infections can be a trigger.
Management includes fluid resuscitation and cautious RBC transfusion (sequestered blood may re-enter the circulation and lead to hyperviscosity). |
| Haemolytic crisis | A rapid fall in Hb due to haemolysis, which can be associated with infections and other sickle crises. Management involves RBC transfusions and treatment of the underlying cause. |
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