Whether it is a human, dog, cat, or even bird or ferret, when sick, their doctors typically draw a blood sample and perform some tests to help determine a diagnosis. These tests are generally one of two types. The first type is the complete blood count (CBC), which determines the number and types of blood cells present. The science concerned with this cellular portion of the blood is called hematology. The second type of test is a blood chemistry panel that measures the quantities of various electrolytes, enzymes, or chemical compounds in the liquid portion of the sample. Sometimes these tests yield little information about the case, but more typically, they are the fastest and best diagnostic tool available to the doctor.
Components of Blood
Blood is made up of a liquid portion plus all the various blood cells. It functions to transport nutrients and oxygen to the cells; wastes and carbon dioxide to the organs responsible for their removal or breakdown; and also to defend the body against bacteria, viruses, and other organisms.
The liquid portion of blood is referred to as plasma, if the blood was not allowed to clot, and serum, if it was. This liquid portion, without the cells, is generally a straw or light yellow color. The liquid portion of the blood is used in the chemistry tests.
Every drop of blood literally contains millions of blood cells. Although the sample drawn for a CBC may seem small, it contains such huge numbers of cells that it is an excellent and accurate portrayal of the total numbers of these cells found in the bloodstream. The CBC is concerned with the quantities and types of red blood cells, white blood cells, and platelets.
Red Blood Cells
First, let us look at the red blood cells (RBC’s). These are the tiny workhorses that are responsible for carrying oxygen to the body’s tissue. RBC’s contain the molecule hemoglobin. Oxygen that is taken into our bodies attaches to the hemoglobin as the RBC’s pass through the lungs. The RBC’s then deliver the oxygen to all the other cells in the body and take the carbon dioxide back to the lungs.
RBC’s are formed in the bone marrow. The bone marrow constantly produces new RBC’s, since the life span of an RBC is only about 120 days. The body can respond quickly to maintain the number of RBC’s present in the blood vessels. The body measures their numbers simply by evaluating the quantity of oxygen being supplied to its tissues. If not enough oxygen is available, then the body sees that as a need for more working RBC’s.
If more RBC’s are needed quickly, then more immature cells (called reticulocytes) are released into the circulation from the bone marrow. However, if there are adequate cells present, it slows down the release of new ones.