Blood test and your child

Introduction

It is important your child is prepared for their blood test as they may have questions, fears, and anxieties. This page will help you explain what will happen during their short visit to the blood clinic.

How is a blood test done?

• Before your child has their blood test we can use a spray that numbs the skin. It works quickly and doesn’t last very long so the bloods will be taken immediately after the child’s skin has been sprayed.
• The nurse will squeeze your child's arm or wrist - this makes the vein fill up with blood and makes it easier for the blood sample to be taken.
• A butterfly needle (small needle) is then inserted into the vein - the needle is connected to a syringe and the blood taken out.
• When the required amount of blood is taken, the needle is removed. The nurse presses on the small wound with cotton wool for a few minutes to stop the bleeding and prevent bruising. A sticky plaster is then put on.
• While the nurse puts the blood into bottles, your child will be encouraged to choose a sticker. This can help them feel they have achieved the goal of having blood taken and to reward them for their bravery.

Why are there so many bottles?

Blood can be tested for many different things. Your child’s doctor will request which tests they want us to take. Different blood bottles are used for different tests - this is why you may see your child’s blood added to bottles of different sizes and colours.

What can I do to help? 

• Keeping your child hydrated reduces the risk of their blood pressure dropping. A drop in blood pressure is the leading cause of fainting and dizziness during blood tests. Being hydrated makes their veins plumper and more visible making it easier for the phlebotomist to find a vein.
• Keep warm. If it is winter or cold outside this can make the veins hide and make it harder to collect a sample. Your child should wear gloves or suitably warm clothing for the appointment.
• If you have been told by your clinician your child should fast before your test (typically for 12 hours) then please bring something for your child to have afterwards. Sugary/sweet snacks are ideal.

Are there any complications?

• Sometimes a bruise develops where the needle was put in. This is much less likely to happen if you press over the site with cotton wool for a few minutes, keeping your child's arm straight. The nurse will do this for you.
• Rarely, some people feel faint during a blood test. Your child (or yourself) will be encouraged to lie down if this happens to prevent fainting.
• Occasionally it can be difficult to find a vein to take the blood from and it may take more than one attempt to get a sample.

When will we get the results?

Results will be passed onto the clinician who requested the tests. They will usually wait until all the results are ready to inform you of the results. Some tests will take longer to process than others – for example, genetic screening can take between 8-12 weeks to be ready.

For further information

Speak to your community midwife, health visitor, GP or ask the nurse you will see in the paediatric outpatient department.

Sources of further information

Blood tests - NHS

Fainting - NHS

Bumps & Bruising - Symptoms & Treatment | St John Ambulance

© North Bristol NHS Trust. This edition published December 2024. Review due December 2027. NBT003753