The complete blood count, called the CBC, is a very common laboratory procedure used in the diagnostic evaluation of numerous conditions in dogs and cats, including many types of infections, anemia, and cancer.  It is also a good tool for routine health monitoring both animals and people.

As its name implies, a CBC is a count of the cells and cellular elements in the blood of dogs and cats, including the numbers of red blood cells, white blood cells, and platelets.  In addition, the size, shape, and other characteristics of the blood cells are described, all of which is important diagnostic information when it comes to your pet's health.

Red blood cells are the most numerous cells in the blood and give blood its red color.  The red blood cells transport oxygen to all tissues of your pet's body using the protein hemoglobin.  The primary role of the white blood cells is to help protect the animal's body against infectious diseases or foreign materials.  The number of white blood cells usually increases with infection, immune diseases, or cancer.  There are several different types of white blood cells (neutrophils, lymphocytes, monocytes, eosinophils, and basophils), and each type has a specific function(s) in both health and disease.  Platelets are small cellular elements that are important for blood clotting; their numbers can also increase or decrease in various clinical conditions.

Only a small sample of blood is needed to perform a CBC.  Your veterinarian or veterinary technician will take a blood sample from a vein in your pet’s leg or neck.  If your pet has a long or extremely thick coat, it may be necessary to shave a small patch of fur so that a vein can be seen more easily.  Most pets don’t even notice having a blood sample taken if someone simply distracts the pet by rubbing its ears during the very short procedure.

After the sample is drawn, pressure will be applied to the area for a minute or so, and a small bandage applied if needed.

The blood is placed in a special tube that prevents it from clotting.  The blood cells and platelets are counted by a piece of specialized laboratory equipment.  A small drop of blood is smeared into a thin layer on a glass slide (blood smear) and stained with special dyes.  The blood smear is then examined under the microscope to evaluate the different types, sizes, shapes, and other characteristics of the blood cells.

Q&A

What exactly is a CBC?

A complete blood count or CBC checks the number, types, and characteristics (eg, size and shape) of cells in the blood, including the red blood cells, white blood cells, and platelets. 

What functions do these cells perform?

Red blood cells transport oxygen to tissues of the body, white blood cells mainly fight infection and cause inflammation, and platelets are important for blood clotting. 

How is this test performed?

Your veterinarian or vet technician will draw a small sample of blood from a vein in your pet’s leg or neck.  The character of the blood cells is checked under a microscope after staining with special dyes, and the numbers of cells are counted using specialized laboratory equipment. 

How is this information used?

The CBC provides important diagnostic clues regarding disorders such as anemia, infection, inflammation, cancer, bleeding disorders, and allergy. 

Written and reviewed by John A. Bukowski, DVM, MPH, PhD and Susan E. Aiello, DVM, ELS