At The Laboratory With My Pet’s Doctor, Complete Blood Count CBC

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Your pet’s doctor finds many reasons to perform laboratory tests for your pet. Sometimes tests are run as a “baseline”, a set of tests by which to measure future performance of the body. That way, if your pet ever becomes ill, he can say, “When he was “x” years of age, “normal” for him was ‘this’, and now we see that the results are ‘that.’” By comparing the differences we might see how function of an organ or organs has deteriorated.

[Companion articles include Chemistry Profile Part 1, Chemistry Profile Part 2 and Urinalysis.]

In this ongoing series of columns on laboratory tests, we will look at individual tests or tests commonly grouped together to see why a doctor might choose them for a patient.

If you’ve ever experienced a serious, debilitating illness, your first stop after leaving the doctor’s office was probably at the lab. Or, you may have been hospitalized and the doctor may have had the lab come to you, to your hospital bedside.

When you get to the lab, how does the technician know what tests to perform? The doctor has defined what is called a “minimum database“. This is comprised of a set of tests that will provide the doctor with enough information to get him on the right track to either confirming a diagnosis he already suspects, or, if he’s not yet sure which of a number of ailments might be your main problem, tests to narrow down the possibilities.

Depending on factors called “signalment“, which include gender, age, height, weight, hair color and race, a minimum database for a young person with a mild illness might include CBC (complete blood count), chemistry profile and urinalysis. Today, let’s learn more about the CBC.. In later columns we will investigate in depth additional common tests that are used.

CBC is a universally used term to refer to the complete blood count. It is “complete” because it examines all of the blood cells circulating in the body. It is a “count” because results report the number of each different kind of cell counted by the laboratory technician.

First, let’s look at red blood cells (RBCs). They are the most numerous cells in the bloodstream, and have as their main duty carrying oxygen and nutrients to all of the parts of the body, in addition to many other important functions. If a patient has too few of them, he is called “anemic.” Anemia has many forms and many causes. The simplest is blood loss anemia, though sometimes the doctor’s challenge is finding out where the blood is being lost! An obvious cause would be blood spilled from a wound in an auto accident. A less obvious cause would be gastrointestinal (GI) loss from stomach ulcers or parasites such as hookworms.

Other forms of anemia are caused by failure of the body to make new red blood cells as rapidly as old ones die or are used up. Many causes exist here, as well, including iron deficiency, bone marrow problems, chronic kidney disease and deficiencies of microminerals.

Now let’s look at the other class of blood cells examined in a CBC: the white blood cells (WBCs). A common one is the Neutrophil, which comes in mature (segmented) and immature (band) forms. Presence of excessive numbers of these in circulation is usually associated with a source of inflammation, sometimes infection, but possibly from other sources of irritation in which infection is not a factor.

The next most numerous WBC in the normal patient is the Lymphocyte. Lymphocytes are cells produced by the immune system and primarily function in fighting illnesses, including cancer, viral disease, bacterial infections, fungal infections inside the body, etc. Numbers of these are increased in certain diseases as the body makes more to keep itself healthy, and decreased when the body is under such great stress that it can’t make enough or when that stress results in the release of large amounts of a natural hormone called “cortisol.” Lymphocytes are also increased in very large numbers in the cancerous disease “lymphocytic leukemia.”

Eosinophils are WBCs that are usually associated with allergic and hypersensitivity reactions. Some allergic patients can have extremely high numbers of these.

Basophils and monocytes are WBCs that play a part in inflammatory conditions. Rarely do they reach great numbers in circulation.

In future editions of “At The Laboratory With My Pet’s Doctor” we will take a close look at the chemistry profile (part one, click here) (part two, click here) urinalysis, thyroid screening tests, fungal assays, electrocardiograms, X-rays and more.
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