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Sickle-cell anaemia - Introduction

NHS Choices Medical Reference

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Sickle cell anaemia is a genetic (inherited) blood disorder in which red blood cells, which carry oxygen around the body, develop abnormally.

Rather than being round and flexible, the sickle red blood cells become shaped like a crescent (or sickle). 

These abnormal red blood cells can then clog sections of blood vessels leading to episodes of pain which can be severe. These episodes are called a sickle cell crisis (also known as a vaso-occlusive crisis).

They can last from a few minutes to several months, though on average most last five to seven days.

The abnormal blood cells have a shorter life-span and are not replaced as quickly as normal; this leads to a shortage of red blood cells, called anaemia. Symptoms of anaemia include tiredness and breathlessness; especially after exercise.

Read more about the symptoms of sickle cell anaemia.


Symptoms of sickle cell anaemia can have a significant impact on quality of life. Potential complications can be life-threatening.

They include:

  • stroke - where the supply of blood to the brain becomes blocked
  • acute chest syndrome - where the lungs suddenly lose their ability to breathe in oxygen; often as a result of infection
  • increased vulnerability to infection
  • pulmonary hypertension - where the blood pressure inside the blood vessels that run from the heart to the lungs becomes dangerously high

However, following improvements in preventative treatment, many complications associated with sickle cell anaemia can be avoided and most people with the condition live much longer than previously.

Read more about the complications of sickle cell anaemia.

When to seek urgent medical advice

Due to the risk of life-threatening conditions, it is important to look out for any signs or symptoms that the patient's health has suddenly deteriorated.

These include:

  • high temperature (fever) of 38C (100.4F) or above
  • severe pain that develops during a sickle cell crisis that cannot be controlled using over-the-counter painkillers, such as paracetamol or ibuprofen
  • breathing difficulties

Read more about when to seek urgent medical advice.

Treating sickle cell anaemia

Treatment helps reduce the severity and frequency of the symptoms of sickle cell anaemia and prevent complications.

In some cases a person with sickle cell anaemia may require regular blood transfusions to help reduce the risks of complications.

Read more about the treatment of sickle cell anaemia.

What causes sickle cell anaemia?

Sickle cell anaemia is caused by a genetic mutation that affects normal development of red blood cells.

A genetic mutation is when the instructions found inside all living cells become scrambled in some way meaning one or more of the processes of the body do not work in the way they should.

The mutation that causes sickle cell anaemia is often referred to as the sickle cell trait.

It is estimated that around a quarter of a million people in England have the sickle cell trait; most of whom have African-Caribbean ancestry.

Having the sickle cell trait itself will not cause a person to develop sickle cell anaemia. But if two people with the trait conceive a child then there is a one in four chance that child will be born with sickle cell anaemia.

Read more about the causes of sickle cell anaemia.


Sickle cell anaemia can be diagnosed with a blood test.

In England, all pregnant women are offered screening (either a blood test or questionnaire) to find out if they are a carrier. If they are a carrier, the baby's father should be offered a screening blood test.  

However, all babies born in the UK are tested for sickle cell anaemia as part of the heel-prick newborn screening test performed by the midwife.

Anyone from at risk groups having a general anaesthetic should be tested for the sickle cell trait or thalassaemia because a general anaesthetic temporarily lowers the amount of oxygen in the blood, which could be dangerous for someone with the condition.

Read more about screening for sickle cell anaemia.

Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Blood vessels
Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessels are veins, arteries and capillaries.
Bone marrow
Bone marrow is the soft, spongy tissue in the centre of bones that produces blood cells.
A disease is an illness or condition that interferes with normal body functions.
Genetic is a term that refers to genes, the characteristics inherited from a family member.
Lungs are a pair of organs in the chest that control breathing. They remove carbon dioxide from the blood and replace it with oxygen.
Oxygen is an odourless, colourless gas that makes up about 20% of the air we breathe.
Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.
Medical Review: February 28, 2012
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