What's in a Blood Test?

Why does your veterinarian recommend routine testing of blood and urine, particularly in senior pets? The goal of every veterinarian is to identify any problems your pet may have very early, when there is a good chance that the disease process can be slowed, or even stopped in its tracks! It is amazing what can be learned about your pet’s health with a few tests conducted on samples of blood and urine.

Drawing the blood sample or catching a bit of urine, that is the simple part of the equation—quick and painless. What happens after your veterinarian obtains samples of your pet’s blood and urine? The blood sample is usually divided into two different types of tubes—a red top and a lavender top. The red-topped tube allows the blood cells to clot so the fluid in the blood, called serum, can be tested for levels of certain chemicals and enzymes. This serum can be put to a number of different tests that will tell your veterinarian how your pet’s internal organs are functioning. Your veterinarian may refer to these tests as a “chemistry panel,” and may even request specific panels that will help to diagnose problems with your pet’s thyroid, kidneys, or liver, just to name a few.

The lavender-topped tube contains a chemical that prevents the blood from clotting so that the red blood cells (which carry oxygen to tissues) and white blood cells (which help fight infections) can be counted. This is called a CBC (complete blood cell count). A drop of this unclotted blood will also be placed on a slide and viewed under a microscope because a lot can be learned from looking at the shape and color of your pet’s blood cells.

And that just covers the basic blood tests. A Senior Blood Panel that includes a urine test (urinalysis) will provide additional information on many health conditions early in the process, when something could be done to slow or stop a disease. Tests conducted on a urine sample will provide information on concentration (called specific gravity), pH (acidic or alkaline), as well as detect items that should not routinely be found in urine (such as protein and glucose). The sediment in the urine also can be examined under a microscope for the presence of bacteria or crystals.

It may seem like the blood and urine samples are taken into the back room and your veterinarian magically appears with results, but the evaluation of these samples is quite sophisticated and reviewing the results is an art in which your vet has been trained. Many veterinary hospitals can conduct several of these blood and urine tests on-site. There are also diagnostic laboratories available that will not only conduct these tests, but that have experts in all areas of veterinary medicine who can consult with your veterinarian.

Depending on the results of the urinalysis, CBC, and chemistry panels, your veterinarian may order additional tests that will be placed in special tubes to preserve whatever chemical he or she wants to measure. When blood and urine tests are combined with other diagnostic tools—such as ultrasound and radiographs—and a physical exam, an accurate accounting of your pet’s health can be established, and any required treatment can be implemented.

The risk for disease increases with the age of your pet. Listed are some common problems found in senior dogs and cats, many of which can be present without your pet showing any outward signs until the disease is quite advanced. So, the next time your veterinarian recommends that blood be drawn for a specific test, remember that early detection makes a difference!

THE OLDER THEY GET: COMMON PROBLEMS IN SENIOR CATS AND DOGS

Cats:

• Overactive thyroid (hyperthyroidism)
• Decreasing kidney function
• Diabetes (especially in overweight cats)
• Fatty liver (lipidosis)

Dogs:

• Underactive thyroid (hypothyroidism)
• Decreasing kidney function
• Overactive adrenal glands (Cushing's disease)
• Diabetes (not just in overweight dogs)
• Liver disease