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Blood Counts


Blood is made up of cells in a liquid called plasma. Blood cells are made in the bone marrow (the soft center of the bones). Then they are released into the body to do their jobs. The body has 3 main types of blood cells: red blood cells, white blood cells, and platelets. This “Do you know” will tell you about normal blood cell counts.

In patients with cancer involving the bone marrow, counting and studying blood cells can tell the staff about a patient’s disease and how to treat it. If all 3 of the blood cell types are studied, the test is called a complete blood count (CBC).

Blood counts are also monitored regularly in all cancer patients since many cancer treatments affect the bone marrow’s ability to make blood cells. Your child may have low blood counts following chemotherapy and radiation therapy. Many different factors help the staff decide whether a patient with low blood counts should be treated before the counts return to normal. Your child’s medical team will assess your child and recommend treatment options.

Red blood cells

Red blood cells contain hemoglobin, a protein which carries oxygen to all parts of the body. We measure the hemoglobin level to check if the body will have enough oxygen for tissues to live and grow. A normal hemoglobin level in healthy people is 12 g/dL. A lower hemoglobin level may cause a patient to have pale skin color and to feel tired and dizzy. Some children become fussy, sleep more, and play less. When the hemoglobin level is very low, your child may need to receive a transfusion of red blood cells from a blood donor.

White blood cells

White blood cells help the body fight infection. The normal white blood cell count in healthy people is 5,000 to 10,000/mm3 . When the white blood cell count is low, it is easier to get an infection and harder to get over it. The staff will measure the white blood cell count often during cancer treatment to see how well a patient can fight off infection. They will let you know if you need to take steps to avoid infection.


A neutrophil is a type of white blood cell that kills bacteria. It is one of the body’s main defenders against infection. Neutropenia occurs when neutrophil counts in the blood are too low. 

Neutropenia is a common side effect of cancer treatment. Chemotherapy (cancer fighting drugs) usually affects the neutrophil count 7 to 14 days after a dose is received. The length of time it takes your child’s blood counts to drop depends on the dose and type of drug used.

Neutrophils are counted as part of the Complete Blood Count (CBC). When checking a patient’s neutrophil count, the medical team relies on a count called the Absolute Neutrophil Count (ANC). The ANC gives an estimate of the body’s ability to fight infection, especially bacterial infections. Your child’s doctor may decide to delay chemotherapy if the ANC is too low.

When the ANC is below 500/mm3 , the risk of infection is high. During these times, it is important to keep your child away from crowds, especially groups of children. In some cases your medical team may decide that your child should wear a face mask (particulate mask) to lower his risk of infection. For more information, see “Do you know… How to use a particulate mask.”

If fever develops while your child is neutropenic (having a low neutrophil count), you need to call his doctor right away. Tests will be done to find the cause of the fever. Your child may be admitted to the hospital for antibiotic treatment and closer monitoring.

Local anesthetics (numbing agents), among other medicines, are used for both nerve block injections and infusions.


Platelets are blood cells that help stop bleeding by making the blood clot. A normal platelet count in healthy people is 150,000 to 400,000/mm3 . Bruising and bleeding often happen when platelet counts are low. A platelet transfusion may be needed when the platelet count is very low.

Some warning signs of a low platelet count include:

  • Tiny red spots under the skin (petechiae),
  • Blood oozing from the mouth and gums,
  • Nosebleeds,
  • Urine that is pink or red, and
  • Stools that are red or black.

Monitoring your child’s blood counts will be an important part of his treatment plan. The medical staff will review these results with you often.


If you have questions about your child’s blood counts or what they mean, please talk to the doctor or nurse. It is important for you to know how these counts affect your child’s health. If you are inside the hospital, dial 3300. Locally, call 901-595-3300. If you are outside the Memphis area, dial toll-free 1-866-2STJUDE (1-866- 278-5833), and press 0 once the call is connected.

This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.

St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.

ATTENTION: If you speak another language, assistance services, free of charge, are available to you. Call 1-866-278-5833 (TTY: 1-901-595-1040).

ATENCIÓN: si habla español, tiene a su disposición servicios gratuitos de asistencia lingüística. Llame al 1-866-278-5833 (TTY: 1-901-595-1040).

تنبيه: إذا كنت تتحدث باللغة العربية فيمكنك الاستعانة بخدمات المساعدة اللغوية المتوفرة لك مجانا. .يرجى الاتصال بالرقم. 5833-278-866-1  (الهاتف النصي: 1040-595-901-1).