Blood Tests & Blood Counts Explained

Why do children need 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.

Why are red blood cells important?

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.

What do white blood cells do?

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.

What do platelets do?

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.

Read more about childhood cancer tests

Read more about childhood cancer