Understanding Your Blood

Perhaps you or someone close to you has been diagnosed with a blood disorder or cancer that disrupts the normal development of blood cells. Your blood cells may not be produced in the right numbers, or they may not function properly. There are several types of blood cells, and some or all of these may be affected depending on your individual condition.

For this reason, your health care provider will regularly monitor your blood counts in a series of tests referred to as a CBC, or complete blood count. The results of these blood tests help your physician determine what is happening within your body. Knowing what these measurements mean will help you understand more about your condition, its symptoms, and how your treatment is working.

Three Main Types of Blood Cells

Red blood cells (RBCs), which give your blood its red color, make up almost half of your blood. RBCs are filled with hemoglobin, a molecule which carries oxygen to the rest of the body. Reticulocytes are young, immature red blood cells that eventually turn into mature red blood cells. All three of these components are monitored.

White blood cells (WBCs) are part of your body’s defense system. These cells help prevent and fight infection. Neutrophils are a type of white blood cell that kill harmful bacteria.

Platelets help stop bleeding and repair damage to your blood vessels by helping to form blood clots.

A Measure of Your Health

Complete blood counts (CBCs) are used to measure how many cells of different types are in your bloodstream. Blood is collected by inserting a needle into a vein and allowing the blood to flow into a tube. The blood sample is sent to the laboratory and the red blood cells, white blood cells and platelets are counted. The CBC is used to test for, diagnose, and monitor many different conditions.

Although everyone has different amounts of blood cells in their body, there is a normal range for each type of blood cell to do its job and keep you well.

Complete Blood Count (CBC) Chart

Test Result

Ref. Range


4.0 - 11.0 


3.90 - 5.20 


12.0 - 16.0 


36.0 - 47.0 


82.0 - 97.0 


27.0 - 33.4 


32.5 - 35.5 


130 - 400 


%  38 - 70 


%  20 - 45 


%  2 - 14 


%   0 - 5 


%   0 - 2 


1.52 - 7.70 


0.80 - 4.95 


0 - 1.54 


0 - 0.55 


0 - 0.22 

This range will vary depending on your age, sex, and many other factors.

Low Counts

The term anemia refers to lower-than-normal amounts of RBCs. Anemia is common in many patients with blood disorders and in cancer patients receiving chemotherapy. Someone who is anemic may feel tired and weak.

“Low white count” means a lower-than-normal number of white blood cells. This makes a person less able to prevent or fight infections. This condition is called leukopenia. Granulocytopenia or neutropenia means a lower-than-normal number of neutrophils, or the white blood cells that kill harmful bacteria.

Patients with low platelet counts have lower-than-normal numbers of platelets. Also referred to as thrombocytopenia, this condition, if severe, may cause a person to bruise and bleed more easily.

Looking at the Bone Marrow

Most blood cells are made in the bone marrow, a spongy material that fills the center of your bones. These blood cells then circulate in a fluid known as plasma. Depending on your condition, you may have many cells in your bone marrow or very few.

Your bone marrow contains important information about blood formation, so it may be monitored by your health care provider. There are two ways this is done: by taking a liquid sample of the bone marrow through a needle, known as bone marrow aspiration, or by removing a small, intact piece of the marrow known as a bone marrow biopsy.