Blood tests are a part of veterinary medicine known as laboratory medicine. Lab findings along with physical examination findings are used to aid, confirm, or disprove a suspected diagnosis. The tests will not usually give an exact diagnosis, but can at least determine if an organ system (i.e., liver or kidney) is not functioning normally or how the body is responding to an infection.

Blood is approximately 60% water, 39% red blood cells (RBC), and the remainder (about 1%) is comprised of hundreds of elements, electrolytes, enzymes, and proteins. There’s about one white blood cell (WBC) for every 100 red blood cells. White blood cells consist of neutrophils, lymphocytes, monocytes, eosinophils, and basophils.

The mechanism by which the horse’s body maintains itself in a stable (and consistent) nature is called “homeostasis.” When all is normal, most of the components of blood are regulated to a very narrow concentration that varies only slightly from horse to horse. Because of that fact, a reference range for what is normal is available for comparison. Many blood components change in a very predictable way relative to a disease process; therefore, blood tests can be extremely valuable aids in disease diagnosis and determining health status.

Complete Blood Count (CBC)

Hematology is used to examine a horse’s red and white blood cell counts. The common name for evaluating these components of the horse’s blood is a complete blood count or CBC. A CBC is a more complete evaluation of the cellular components.

The different types of WBCs are counted on the “differential” (the part of the test that counts the different types of cells) and are evaluated as a percentage of the total. Looking at the total WBC count and the differential can help diagnose various types of inflammation. For example, with severe acute inflammation/infection, the WBC count might decrease with the appearance of immature neutrophils. With more slowly developing or chronic inflammation/infection, the total WBC count tends to increase. With allergic-type inflammation, increases in the numbers of eosinophils and basophils might be noted. The monocyte is the “clean-up” cell of the body, so with chronic inflammation there usually is an increase in the number of monocytes.

The WBC count is also useful in determining if you are getting a response to treatment. For example, with a mild/ moderate case of pneumonia, you would expect an increase in the WBC count. If the antibiotic of choice is correct, you would expect—in addition to improvement in the clinical signs—the WBC count to decrease toward the normal range.

If the infection is extremely intense and involves a vigorous bacteria (or virus), the WBCs are consumed rapidly and the total count decreases because consumption exceeds production. With less intense and more chronic infections, the WBC count increases.


Often performed as either a general checkup or if there is an indication such as increase urination, increase frequency of urination, change in color, blood in urine, difficulty urinating. The UA can help determine if there is an increase amount of crystals in the urine, if a lower urinary tract infection exists or if there is loss of protein or sugar in the urine,

Cushings test:

In this day of our horses living longer cushings and metabolic disease seem to be more common than ever. Depending on circumstances a variety of test can be done to check Cushings or ED status. These include: Diurnal cortisol and insulin levels. Resting ACTH levels, resting unsulin levels, glucose and leptin values. Tyroid responsive hormone and thyroid levels.

Hormone evaluation:
Whether it’s a pregnancy check or getting your mare to breed, bloodwork to check progesterone and estrogen levels can be evaluated quickly. If your mare is overly aggressive a bloodtest can determine if there is a tumor causing increased testorene present. If you have a stallion that isn’t quite performing to snuff we can check his testosterone levels as well.

Take-Home Message

Blood testing can provide important information, but it almost always needs to be interpreted relative to the clinical examination findings, history, and additional testing in order to arrive at an accurate diagnosis of the problem.

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