Haematology - Sickle cell anaemia

Question 1

What is the pathophysiology of sickle cell anaemia?

Answer 1

Genetic condition that causes sickle-shaped RBCs

Patients with sickle-cell disease have an abnormal variant called haemoglobin S (HbS).

HbS causes red blood cells to be an abnormal “sickle” shape.

Question 2

What is the genetic inheritance pattern of sickle cell?

Answer 2

Autosomal recessive

Abnormal gene for beta-globin on chromosome 11.

One copy only of the abnormal gene = sickle cell trait

Question 3

Diagnosis

Answer 3

Tested in the new-born screening heel prick test at 5d

Also tested for in pregnant women at risk of being carriers of the sickle cell gene

Question 4

Complications of sickle cell anaemia?

Answer 4

Anaemia

Increased risk of infection

Stroke

Avascular necrosis in large joints such as the hip

Pulmonary hypertension

Painful and persistent penile erection (priapism)

Chronic kidney disease

Sickle cell crises

Acute chest syndrome

Question 5

General management of sickle cell disease

Answer 5

Avoid dehydration and other triggers of crises

Ensure vaccines are up to date

Antibiotic prophylaxis to protect against infection with penicillin V (phenoxymethypenicillin)

Hydroxycarbamide can be used to stimulate production of fetal haemoglobin (HbF). (Fetal haemoglobin does not lead to sickling of red blood cells. This has a protective effect against sickle cell crises and acute chest syndrome.)

Blood transfusion for severe anaemia

Bone marrow transplant can be curative

Question 6

Sickle cell crises triggers

Answer 6

Can be spontaneous or triggered by:

• Infection
• Dehydration
• Cold
• Significant life events

Question 7

How are sickle cell crises generally managed?

Answer 7

Have a low threshold for admission to hospital

Treat any infection

Keep warm

Keep well hydrated (IV fluids may be required)

Simple analgesia such as paracetamol and ibuprofen

Penile aspiration in priapism

Question 8

What are the types of crises?

Answer 8

Vaso-occlusive crisis (painful crisis)

Splenic sequestration crisis

Aplastic crisis

(Also hyper-haemolytic)

Question 9

What occurs in vaso-occlusive crisis of sickle cell disease?

Answer 9

Sickle cell RBCs block capillaries causing digital ischaemia

It is associated with dehydration and raised haematocrit.

Symptoms are typically pain, fever and those of the triggering infection.

It can cause priapism in men by trapping blood in the penis causing a painful and persistent erection. This is a UROLOGICAL EMERGENCY and is treated with aspiration of blood from the penis.

Question 10

What occurs in a sequestration crisis?

Answer 10

RBCs blocking blood flow in the spleen

Causes enlarged and painful spleen

Pooling of blood can lead to severe anaemia and hypovolaemic shock

It is therefore an EMERGENCY.

Question 11

Management of sequestration crisis

Answer 11

Supportive management with blood transfusions and fluid resuscitation to treat anaemia/shock

Splenectomy for recurrent crises as this prevents sequestration

Question 12

What occurs in aplastic crisis?

Answer 12

Temporary loss of creation of new RBCs

Commonly triggered by parvovirus B19

Significant anaemia

Question 13

Management of aplastic crisis?

Answer 13

Supportive with blood transfusions if needed

It usually resolves spontaneously within a week.

Question 14

Acute chest syndrome diagnostic criteria

Answer 14

Diagnosis is if there are:

• Fever or respiratory symptoms with
• New infiltrates seen on a chest x-ray

Question 15

What can cause acute chest syndrome?

Answer 15

This can be due to infection (e.g. pneumonia or bronchiolitis) or non-infective causes (e.g. pulmonary vaso-occlusion or fat emboli).

Question 16

Management of acute chest syndrome

Answer 16

MEDICAL EMERGENCY

Early supportive management and treatment of underlying cause:
- Antibiotics/antivirals for infections
- Blood transfusions for anaemia
- Incentive spirometry using a machine that encourages effective and deep breathing
Artificial ventilation with NIV or intubation may be required