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Blood counts for hematology patients


What are blood counts?

Blood is made up of cells and a liquid called plasma. Your blood cells are made in the soft center of your bones, called the bone marrow. From there, they go into your bloodstream.

Your body has 3 main types of blood cells. These are red blood cells, white blood cells, and platelets.

Counting and studying blood cells gives the medical team information about your child’s disease. They use a common test called a complete blood count or “CBC.” This handout tells you what this test studies and what the results mean.

Red blood cells

Red blood cells carry oxygen around the body. The part of the red blood cell that carries oxygen is called hemoglobin (“HEE-muh-glow-bin”). Having less hemoglobin or fewer red blood cells than usual is called anemia (“uh-NEE-mee-uh”).

The results of a complete blood count, or CBC, show the amount of hemoglobin in the blood. People without a blood disorder have a level of 11 to 15. If your child’s level is lower, they might:

  • Look pale
  • Feel tired, dizzy, or weak
  • Act fussy
  • Sleep more and play less

Your child might need to get extra red blood cells from a donor if their hemoglobin is very low. This is called a transfusion.


A reticulocyte (“reh-TICK-you-low-site”) is a new red blood cell that is still forming in the bone marrow. Normally, reticulocytes stay in the bone marrow until they develop into red blood cells and enter the blood. You do not have many reticulocytes in your bloodstream if you are healthy, because they are in your bone marrow.

If your child’s reticulocyte count is higher than normal, their body is making more red blood cells due to anemia (too few red blood cells or too little hemoglobin). If your child has a low reticulocyte count, their body is making fewer red blood cells than normal. This could be dangerous. We will test your child's reticulocyte count at each clinic visit.

White blood cells

White blood cells help your body fight infection. A person without a blood disorder has white blood cell count that ranges from 5,000 to 10,000. It is easier to get an infection and more difficult to recover from it if your white blood cell count is low. However, illness and some medicines can make the white blood cell count go up or down for a short time.

Low neutrophils (neutropenia)

A neutrophil is a type of white blood cell that kills germs called bacteria. Neutrophils help prevent infections. If your child does not have enough neutrophils, this is called neutropenia (new-tro-PEE-nia).  

We use a measurement called the absolute neutrophil count, or ANC, to keep track of your child's neutrophils. The ANC shows how well the body can fight infections, especially from bacteria. When the ANC test result is below 500, your child is at high risk for infection. During these times, it is important to keep your child away from crowds, especially groups of children. The medical team might have your child wear a face mask to lower the risk of infection.


Platelets are blood cells that help stop bleeding. They do this by making the blood clot, or clump up so it stops flowing. A person without a blood disorder has a platelet count of about 150,000 to 400,000.

The medical term for having too few platelets is “low platelet count,” or thrombocytopenia (throm-bow-SIGH-toe-PEE-nee-uh). Your child might need to get extra platelets from a donor if their platelet level is very low. This is called a transfusion. Some warning signs of a low platelet count include:

  • Bruising or bleeding more easily than usual,
  • Flat red spots under the skin called petechiae (puh-TEEK-ee-ay),
  • Bleeding from the mouth and gums,
  • Nosebleeds
  • Urine (pee) that is pink or red, or
  • Bowel movements (poop) that are red or black.

If your child hits their head, contact us immediately to have them checked. They are at risk of bleeding more easily than other children.

Keeping track of your child's blood counts

We will keep track of your child’s blood counts. They usually have a CBC and reticulocyte count at each clinic visit. The doctor will tell you if your child needs more blood tests.

Keeping track of your child's blood counts is an important part of treatment. We will talk about the test results with you and give you a copy each time your child sees the doctor. You should keep these results with your child's medical records.


If you have questions about your child's blood counts or what they mean, ask the doctor or nurse. You may also call the St. Jude operator at (901) 595-3300 or toll-free 1-866-2STJUDE (1-866-278-5833) and ask for your child's nurse case manager.


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).

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