Complete Blood Count Tests

Most childhood cancer patients have regular complete blood count (CBC) tests during their treatment.

Cancer therapies such as chemotherapy and radiation therapy may affect the bone marrow’s ability to make blood cells. Regular complete blood count tests help the care team monitor the patient’s health and ability to fight off infections. When counts are low, the care team can provide treatment.

In patients with cancer involving the bone marrow, counting and studying blood cells provide information about the patient’s disease and how to treat it.

What Happens During Complete Blood Count Test

For a complete blood count test, a health care provider will take a sample of blood. If the patient has a central venous access device (central line, port, or peripherally inserted central catheter (PICC)), the blood may be taken from it. If the patient does not have such a device, the provider may start a peripheral IV or draw blood by inserting a needle into a vein and collecting the blood in attached vials or tubes (venipuncture).

Types of Blood Cells and Related Conditions

Blood contains 3 different types of blood cells along with plasma, the liquid portion of blood. Low numbers of blood cells can lead to serious health conditions such as neutropenia, anemia, and thrombocytopenia.

Red blood cells and anemia

Red blood cells carry oxygen to tissues and organs. A lower than normal red blood cell count results in anemia. Signs and symptoms of anemia include fatigue, shortness of breath, dizziness, headaches, a fast heartbeat, and/or pale skin. Patients with this condition may need a transfusion of red blood cells.

Platelets and thrombocytopenia

Platelets help the blood clot. A lower than normal platelet count results in thrombocytopenia. Signs and symptoms of thrombocytopenia may include unusual bruising, tiny spots under the skin (petechiae), urine that is pink or red, and stools that are red or black. A platelet transfusion may be needed when the platelet count is low. 

White blood cells and neutropenia

White blood cells fight infection. A lower than normal white blood cell count affects the body’s ability to fight off invading bacteria, fungi, viruses, and foreign substances. A low count of a type of white blood cell called a neutrophil can result in a condition called neutropenia, which may require hospitalization.

What a Complete Blood Count Test Measures

A complete blood count test measures:

• Red blood cells (RBC) – The numbers, size, and types of red blood cells
• White blood cells (WBC) – The numbers and types of white blood cells
• Platelets – The numbers and size of the platelets
• Hemoglobin – An iron-rich protein in red blood cells that carries oxygen
• Hematocrit – How much space red blood cells take up in the blood
• Reticulocyte count – Number of young red blood cells in the blood
• Mean corpuscular volume (MCV) – The average size of red blood cells

Complete Blood Count with Differential

A complete blood count with differential also includes tests for the different types of white blood cells:

• Neutrophils – These cells are the most common type of white blood cell. They travel to the site of an infection and release substances called enzymes to fight off invading viruses or bacteria. One measurement of neutrophils is the absolute neutrophil count, also known as ANC. Knowing the ANC count helps show how well the immune system can fight infection.
• Lymphocytes - There are two main types of lymphocytes: B cells and T cells. B cells fight off invading viruses, bacteria, and toxins. T cells target and destroy the body's own cells that have been infected by viruses or cancer cells.
• Monocytes – These cells remove foreign material, remove dead cells, and boost the body's immune response.
• Eosinophils – These cells fight infection, inflammation, and allergic reactions. They also defend the body against parasites and bacteria.
• Basophils – These cells release enzymes to help control allergic reactions and asthma attacks.

Normal ranges for these different types of blood cells can vary widely depending on the child’s age. The care team may review these results with families often.

Monitoring blood counts is an important part of a patient’s treatment plan.