Key points about blood tests for children and young people with cancer
- your child will have regular blood tests - at the time of diagnosis, during their treatment and after treatment
- a nurse, phlebotomist (someone trained to take blood from a patient) or doctor will take your child's blood and send it to the laboratory to be studied
- your child's doctor or nurse will tell you what your child's blood test results are and what they mean
Regular blood tests
Your child will have regular blood tests - at the time of diagnosis, during their treatment and after treatment. The haematology department counts the blood cells.
The blood count is one of several ways of monitoring the effects of your child's treatment. Your child's doctor or nurse will tell you what your child's blood test results are and what they mean.
Scientists who study tiny organisms (microbiologists) may check the blood to see whether there is an infection. This is called a blood culture.
The chemistry laboratory measures salts and chemicals in the blood sample. This gives information about how your child's kidneys and liver are functioning.
If your child needs a blood transfusion, blood samples can also help cross-match blood.
Having a blood test
A nurse, phlebotomist (someone trained to take blood from a patient) or doctor will take your child's blood and send it to the laboratory to be studied. Your healthcare team may ask you to take your child to a community blood testing centre. This allows the result to be available and acted on before your appointment. This allows treatment to be more streamlined for you and for the healthcare team.
A nurse or phlebotomist will use a small finger prick to take blood. On some occasions, a nurse may take blood tests from the central venous line (CVL). If a finger prick won't provide enough blood for the test, and there is no CVL in place, a doctor or nurse will use a needle and syringe to take the blood from the vein.
The doctor or nurse will put a pain-relieving cream or gel on your child's skin before the blood test. This numbs the skin, so your child won't feel the needle prick.
Blood test results
It's a good idea to keep your child's test results together in a folder. After your child's doctor or nurse has explained the tests your child will need, be sure to ask for further information if you want to understand more.
Why children with cancer need blood tests
Chemotherapy works by killing cells that grow quickly, such as cancer cells. However, it also kills other good cells that are growing fast, such as blood cells that grow in bone marrow.
Your child's healthcare team will order regular blood tests to find out if they need to treat a low blood count and to know when it is safe to give the next dose of chemotherapy.
Your child may not have to go to the hospital for every blood test. Sometimes they can be done at your local community laboratory.
The role of red blood cells
Red blood cells contain haemoglobin (Hb), which carries oxygen from the lungs to the rest of the body. Haemoglobin levels reveal how many red blood cells there are.
When the haemoglobin level is low, this is called anaemia. Your child may look pale, feel tired, dizzy or be short of breath. Call the hospital if you see these signs or if you are concerned.
When your child's haemoglobin is low, they may need to go to the hospital for a blood transfusion. After a transfusion, your child will look less pale and have more energy.
The role of white blood cells
White blood cells fight infection. The most important white cells are called neutrophils. They fight bacterial infections. When the neutrophil count is low, this is called neutropenia.
If your child's neutrophil level is low, they will be at risk of getting a serious bacterial infection.
If your child has a temperature of 38 degrees Celsius or above, you must call the hospital immediately. Your child needs medical attention.
The role of platelets
Platelets help make clots to stop bleeding. When your child's platelet count is low, this is called thrombocytopenia. Sometimes if your child's platelet count is too low, they may need a platelet transfusion.
Some signs that your child has a low platelet count are:
- increased bruising
- nose bleeds
- bleeding gums
- tiny red spots that suddenly appear on the skin (these are small bruises)
Call the hospital if your child has any of these symptoms or if you are concerned.
If your child has a temperature of 38 degrees Celsius or above, you must call the hospital immediately. Your child needs medical attention.
Acknowledgements
All the pages in the childhood cancer section of this website have been written by health professionals who work in the field of paediatric oncology. They have been reviewed by the members of the National Child Cancer Network (NZ). Medical information is authorised by the clinical leader of the National Child Cancer Network.
