Last post we introduced the most common "blood" test; the CBC, or complete blood count. We focused on the analysis of red blood cells in the first post and today we'll cover the white blood cells (WBC"S).
White blood cells, or leukocytes, come from the lymph nodes and bone marrow. These cells are important components of our disease fighting immune system. There are five different types of white blood cells including neutrophils, lymphocytes, monocytes, eosinophils and basophils.
The absolute number and the proportion of each cell type and even the stage of maturity of the cells can tell us a great deal about the state of a pet's health and how the body is responding to a potential disease process.
The process of examining the different WBC's is called a differential analysis and this differential can tell us a good deal about what might be happening in the body.
The most numerous type of WBC is the neutrophil. These cells are the first line of defense against bacterial invaders, and in the presence of an acute infection the numbers and proportion of neutrophils to other WBC's will increase. If the infection is severe we may see increasing numbers of immature neutrophils. This is called a "left shift" and indicates that the an infection is in progress and the body is producing neutrophils at a rapid rate in response..
Neutrophils increase in response to infection, inflammation, exercise and the use of corticosteroids. They decrease in number and proportion with some viral infections, cancer chemotherapy drugs, and with bone marrow disease.
Lymphocytes are also important disease fighting cells. These cells produce antibodies against infectious agents like bacteria and viral invaders. Lymphocytes are divided into T-cells and B- cells and each type has an important role in the immune response. Lymphocytes increase in response to most infections, especially viral infections. Lymphocytic leukemia is also a common cause of significant increases in lymphocytes.
They may decrease in number in response to cortisone like drugs, chronic stress and certain conditions involving diarrhea.
Monocytes are the largest white blood cell type and they may increase in the presence of a chronic infection that has been going on for a long time. They may be elevated due to chronic inflammation too. These cells normally only make up 2-8% of white blood cells.
Animals with allergies or parasitic infections may have increased numbers of eosinophils and basophils. Both internal parasites and ectoparasites like fleas can lead to higher numbers of these cells.
If your dog or cat develops a sudden illness and the signs are non specific, like lack of appetite, lethargy, maybe some vomiting and diarrhea, your Vet will most likley order a CBC with a differential. He or she will learn a great deal about what is going on with this test and the results will help guide the diagnosis.
Subsequent tests, like serum chemistry tests that evaluate the function of various organ systems are up next. These test help zero in on what is actually wrong with the pet.
Stay tuned.