Transcranial dopplers (TCD)

What is a transcranial doppler?

A transcranial doppler (TCD) is a test to measure the blood flow inside the brain. In sickle cell disease, the blood vessels in the brain can get narrower, which increases the risk of having a stroke.

Around 11 percent of children with sickle cell disease will have a noticeable (overt) stroke by the age of 20.

Around 9 percent of children with sickle cell disease will have a ‘silent’ stroke which are only detected by special tests.

The transcranial doppler test aims to find out who is at highest risk of having a stroke so we can try to reduce this risk.

How is a transcranial doppler done?

A transcranial doppler test uses ultrasound (like the test to see an unborn baby in the womb). It measures the speed of blood flow in the blood vessels in the neck and head. If the blood is travelling faster than usual, it suggests the blood vessels are narrow.

Will it hurt?

Having a transcranial doppler test does not hurt. The test takes about 30 minutes and is done in the X-ray department. We encourage you to stay with your child during the test.

There are no known risks from having a transcranial doppler.

We aim to do a transcranial doppler test once a year in all children with sickle cell disease. You will be sent an appointment for this.

Please let us know if your child has been unwell (with a fever or other signs of infection) in the days leading up to the scan.

What do the results mean?

If the transcranial doppler is not normal, this means that your child has narrowed blood vessels in their brain. This means they have a higher chance of having a stroke than a child who has a normal test results.

If we know that your child has a higher risk of stroke, it allows us to offer treatment to try to prevent this.

What preventative treatment is available?

Studies have shown that children with abnormal test results who have regular blood transfusions, have a lower chance of having a stroke than children who do not have regular transfusions. The transfusions are thought to work by reducing the proportion of sickle haemoglobin in the blood stream, allowing the blood to flow more freely.

How often are transfusions needed?

If a child starts on a regular transfusion programme, they usually need a transfusion once every 4 weeks.

This will be done as a day case and will not need to stay overnight in hospital. The transfusion will be given in the haematology outpatient department and will take most of the day. While your child is having their transfusion, they can still move around and play, or go to the school room, but they will be attached to a drip.

In some children it can be difficult to get the drip into the vein every month, and a more permanent device called a port-a-cath may be needed to allow us to give the blood transfusions without causing your child distress.

Helpful things about regular blood transfusions

Preventing strokes

A stroke is caused by the brain not getting enough oxygen. It can be very serious and cause long term problems such as:

• arm or leg weakness
• walking difficulties
• loss of speech
• loss of vision

Sometimes a child with sickle cell disease can die of a stroke.

An international trial of around 130 children showed that regular blood transfusions reduced the risk of stroke by 90 percent.

Those children with abnormal transcranial doppler test results who did not have transfusions, had a 16% chance of having a stroke. Those who did have transfusions had a 1.6 percent chance of having a stroke.

This means that if we give blood transfusion to 7 children from the ‘at risk’ group regularly, 1 of those children would avoid a stroke. The other 6 children will have been transfused but would never have had a stroke anyway.

At the moment, we cannot predict exactly which children will have a stroke and which will not, which is why we offer regular transfusions to all children with an abnormal transcranial doppler test results.

Prevention of other sickle problems

Regular transfusion programmes often help other sickle problems such as pains, tiredness, and chest crisis.

Difficult things about regular transfusions

Having to attend for transfusion

We try to arrange this so your child misses as little school as possible. Your child will need someone to bring them to and from the hospital. We advise that someone stays with the child during their transfusions, particularly if they are very young.

Iron overload and iron chelation

The major problem with blood transfusions is that they contain lots of iron. Our bodies have no way to get rid of this much iron and so it builds up inside people who have lots of transfusions. If this iron is not removed with special medication, it will eventually cause serious damage to the liver, heart, and other vital organs.

It will be essential that your child takes regular medications whilst they are on transfusions to prevent iron build up. For many children, these medications can be tablets which can be swallowed whole or crushed in food. Some children may need to use a medicine which is given through a small needle into the skin via a continuous pump overnight (at home) 3 to 5 times per week.

Alloimmunisation

Children who have had lots of blood from other people can make antibodies to certain types of blood. If this happens they cannot have that type of blood again. If children make too many antibodies, it can be difficult to find blood that is suitable for them.

We try very hard to give all our children with sickle cell disease blood that is very closely matched to their own to prevent the formation of antibodies.

Infection

There is a small risk of getting an infection from a blood transfusion. This is very rare and all blood in the UK is carefully tested to make this risk as low as possible.

What are the alternatives?

Children with an abnormal transcranial doppler test results do not have to start transfusions, but there is no other treatment to reduce the risk of stroke in sickle cell disease.

Below are alternative therapies which may be considered. We can discuss these with you further at your clinic appointment. 

Surgery

Some children, may only have 1 very small section of narrowed blood vessels, so surgery may be the best option. If this is possible with your child, you will be referred to the vascular neurosurgery specialist to discuss the options.

Hydroxycarbamide

Hydroxycarbamide is a medication that has been used to treat a range of blood conditions for a number of years and has been shown to reduce some of the complications of sickle cell disease. It is taken by mouth once a day.

Hydroxycarbamide therapy has not been formally tested as first line therapy for children with an abnormal transcranial doppler test result. However, a number of studies have shown that hydroxycarbamide can reduce the speed that the blood is pumped through the blood vessels.

There is data to support that switching from regular transfusions to hydroxycarbamide can be helpful if a child has received at least one year of regular transfusions, and they have has no severe vasculopathy identified on MRI scan.

There is also data to show that children who have conditional range transcranial doppler velocities can be treated with hydroxycarbamide therapy to help prevent progression from conditional to abnormal transcranial doppler velocity.

What if I cannot decide what to do?

Starting transfusions can seem like a big decision, particularly if your child has had very few problems so far from their sickle cell disease. Sometimes it can be helpful to have an MRI brain scan to see in more detail what effect narrowing blood vessels has had on the brain tissue. This will be recommended if the transcranial doppler test results are abnormal.

We understand that you will be worried and upset if your child is found to be at higher risk of stroke. We hope you find this information helpful but it is not intended to replace the explanation and discussion that will be given by your consultant. If you have any questions or concerns please ask the team in clinic for further information.