What is sickle cell anaemia?

Sickle cell anaemia is an inherited blood disorder in which red blood cells develop abnormally. 


  • Sickle cell anaemia is caused by a mutation in a gene called haemoglobin beta (HBB), located on chromosome 11.
  • It is a recessive genetic disease, which means that both copies of the gene must contain the mutation for a person to have sickle cell anaemia.
  • If an individual has just one copy of the mutated gene they are said to be a carrier of the sickle cell trait.
  • If both parents are carriers there is a chance their child could be born with sickle cell anaemia.


  • The HBB gene codes for haemoglobin, a protein in red blood cells that carries oxygen around the body .
  • A mutation in HBB results in a change in one of the bases in the DNA sequence from an A to a T.
  • This then changes the amino acid in the haemoglobin protein from glutamic acid to valine.
  • This causes the body to produce a new form of haemoglobin called HbS, which behaves very differently to regular haemoglobin (HbA).
  • HbS causes the red blood cells to develop abnormally and become sickle-shaped (rather than the usual doughnut shape), harder and less flexible.
  • This means that they can become stuck in the blood vessels, causing blockages.
Illustration showing the difference between normal red blood cells and sickle red blood cells.

Illustration showing the difference between normal red blood cells and sickle red blood cells.

Image credit: Genome Research Limited


  • The symptoms of sickle cell anaemia vary considerably from person to person.
  • Pain develops when sickle-shaped red blood cells block the flow of blood to the chest, abdomen and joints.
  • These spells of pain are called 'sickle cell crisis' and can last anything from a few minutes to several months.
  • Symptoms can have a significant impact on quality of life and can lead to life-threatening complications such as:
    • 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 as a result of sickle cells blocking blood vessels in the lungs.
    • increased risk of infection: sickle cell anaemia can damage the spleen, a key organ involved in fighting infection.
    • pulmonary hypertension: where sickle-shaped red blood cells block the flow of blood from the heart to the lungs causing the blood pressure in these vessels to become dangerously high.
  • Sudden deterioration may be characterised by:
    • high body temperature of 38˚C or above
    • severe pain that cannot be controlled with paracetamol or ibuprofen
    • difficulty breathing.
  • Methods to deal with sickle cell anaemia have improved dramatically in recent years, so serious complications rarely occur and people now live much longer than they used to.
  • 40 years ago, few people lived past their teenage years and many died before the age of two years. The main cause of death was bacterial infection.
  • Now, most affected people are expected to live to about 40 or 50 years old. The main causes of death are infections and stroke.


  • Sickle cell anaemia is diagnosed using a blood test which detects the presence of the abnormal HbS haemoglobin in the red blood cells.
  • In children the blood is taken by pricking a finger or heel.
  • In adults the blood is drawn from a vein in the arm.
  • The blood sample is analysed to see if the abnormal HbS haemoglobin (rather than normal HbA haemoglobin) is present.


  • Most treatments aim to treat the individual symptoms of sickle cell such as anaemia.
  • Treatment plans require a number of different healthcare professionals working together, such as haematologists (specialists in blood disorders), clinical psychologists, social workers and physiotherapists who can help patients with pain monitoring and relief.
  • Regular blood transfusions can help reduce the risk of complications, such as stroke, by up to 90 per cent.
  • However, chelation therapy may need to be given after transfusion to remove excess iron from the patient’s body. This excess iron can lead to complications including liver cancer, diabetes and infections.
  • Daily antibiotics, such as penicillin, are often given to help protect against serious infections in children aged under five years.
  • Pain relief is provided to reduce the pain associated with sickle cell crisis.
  • Lifestyle advice, such as drinking plenty of fluids, is given to help reduce the risk of sickle cell crisis.
  • If individuals continue to experience pain, a medication called hydroxycarbamide may be offered, to be taken once a day.
    • This drug works by stimulating the body to produce another type of haemoglobin, called foetal haemoglobin.
    • Foetal haemoglobin is not affected by the mutation that causes sickle cell anaemia.
    • Foetal haemoglobin can substitute for the adult haemoglobin to carry oxygen around the body and help reduce the risk of a sickle cell crisis occurring.
  • The risk of an individual developing complications can also be assessed to help prevent them occurring.
    • A child’s risk of a stroke can be assessed using a test known as a Transcranial Doppler scan that measures the rate of blood flow in blood vessels in the head and neck, which supply blood to the brain.
    • If the arteries are narrow, which can increase the risk of having a stroke in the future, blood travels faster and makes a high pitched noise that can be detected by the scanner.  
  • Blood and bone marrow stem cell transplants may offer a cure for a small number of people.


  • In the UK, all pregnant women are asked to answer a questionnaire to assess their risk of carrying a baby with sickle cell anaemia.
  • Pregnant women may also be offered a blood test to find out if they are a carrier of the faulty HBB gene that causes sickle cell anaemia.
  • If they are found to be a carrier, the baby’s father is then offered a blood test too.
  • If both parents are carriers there is a chance the baby will be born with sickle cell anaemia.
  • All babies in the UK are tested for sickle cell anaemia after birth through the heel-prick newborn screening test.
  • Anyone from at risk groups having a general anaesthetic is tested for sickle cell anaemia. This is because general anaesthetic reduces the amount of oxygen in the blood, which could be dangerous for someone with the condition.

This page was last updated on 2017-05-17