When presented with a horse with a physical or medical problem, the most common method of making a diagnosis, formulating a treatment plan and offering a realistic prognosis is to secure a careful history and perform a complete physical examination. Other tests or procedures that may add information to the case are called "ancillary procedures".  The most common of these ancillary tests is what is generally called "blood work".

Falling within the heading of "blood work" is usually what is called a CBC and differential. CBC stands for complete blood count  and includes the following values: 

a) hemaglobin (this is the protein found within the red blood cells that carries oxygen)

b) hematocrit (this value tells whether the horse may be anemic or dehydrated)

c) WBC and RBC counts (this tells the number of white and red blood cells present)

d) platelet count (platelets are responsible for proper blood clotting)

The "differential" part of the CBC counts the different types of white blood cells. There are 5 general classes of white blood cells including neutrophils, basophils, eosinophils, monocytes and lymphocytes.

Problems that can be elucidated from the CBC and differential include anemia, dehydration and bacterial and viral infections.Another group of tests included under "bloodwork" are the serum chemistries. These are groups of tests that evaluate organ functions, including liver, kidneys, muscles and electrolytes (including calcium, sodium, potassium, chloride and glucose). Results are usually available within 24 hours.

 While the CBC and differential is by far the most common type of  "blood work" perfomed there are a large number of condition specific tests that can be done on a blood sample. These condition specific tests include those for diseases such as Lyme disease, Cushings disease, EPM, West Nile Virus, equine infectious anemia (EIA), thyroid disease, pregnancy diagnosis, ovarian tumor diagnosis, etc.

The next time then that your veterinarian says "let's take some blood"  you should be able to have a discussion as to what tests will be done and why.