Blood Test Basics

When the Vet tells you they’re going to do some bloodwork, what does that really mean? We all know it means a tech will probably come into the room and hold your pet steady while the vet draws one or more syringes worth of blood from the animal’s vein. It may be taken from a front or a rear leg, depending on the pet’s size and disposition and the quality of the veins.

But what happens after that blood leaves the exam room? What kinds of tests can be done on blood and how do we know why certain tests are necessary? And how can we learn to interpret blood test results ourselves, so we can better understand our pet’s condition and participate more effectively in treatment when it’s required?

One of the most common and most essential blood tests done on dogs is the 4DX snap test. That’s slang for a chemical test done with a plastic disposable device that has a bit of fresh blood applied to it. The 4DX tests for four different conditions that are now common in our region: Heartworm, Lyme Disease, Anaplasmosis and Ehrlichia. The last three in that list are tick-borne viruses; they result from the injection of tick saliva into the animal’s bloodstream. Heartworm is spread by a bite from a mosquito.

Caught early, all the tick-borne diseases discovered by a 4DX can be treated by antibiotics and brought under control. If these viruses are not caught early and treated, serious disability, organ damage and even death can follow. Heartworm caught early can also be treated effectively, but it is a much more involved treatment and far more costly than treating the tick-borne viruses. The bottom line: a simple 4DX test every year or two saves money and lives.

When it comes to blood tests common to most species, we need to think about the CBC and the Blood Chemistry tests.  These are the tests that help a vet determine what may be happening inside the animal. After all, a vet is at a disadvantage in attempting to uncover the cause for your pet’s overt symptoms. If Fluffy is suffering from chronic diarrhea, or is lethargic, or urinating rainbow colors, she can’t tell us verbally that she drank from a stinky puddle this morning or has been infected by a parasite. But conditions like anemia, infection, inflammation, dehydration, cancer, immune-mediated disease, kidney and liver deficiencies are all signaled by the blood. A blood test is a snapshot in time of the animal’s internal chemistry. It may need to be run more than once over time to reveal trends in recovery or decline of the animal’s condition. And sometimes follow-on testing needs to be done to further describe a condition; but it’s the CBC and Blood Chemistry panels that are the first-line detectives.

There are five parameters the vet is evaluating in the CBC & Chemistry: red blood cells, white blood cells, serum (AKA plasma), fibrinogen, and platelets. The results will usually show two columns or graphics: one lists your pet’s level for each parameter, the second lists the normal ranges for those parameters so you can compare your pet’s results with what we consider normal. Here’s a crash course in what the results of each parameter can mean:

Red Blood Cells: too many of these is typically associated with dehydration; too few usually means anemia. Red blood cell shape and size also can tell a vet about underlying conditions that may be at work in your pet, and some parasites can also be detected in the red blood cells.

White blood cells: too many? Infection likely; too few? Auto-immune disease possibility. The shape of white blood cells can signal certain blood cancers as well.

Platelets:  Too few platelets can indicate presence of a tick-borne virus like anaplasmosis or ehrlichia or an auto-immune disease like immune mediated hemolytic anemia (IMHA).

Fibrinogen:  Elevated levels indicate infection or inflammation.

Serum/Plasma: Altered levels can indicate kidney or liver damage, metabolic abnormalities, or tissue damage. Changes in electrolytes, glucose, proteins, bilirubin, enzymes, BUN (blood urea nitrogen) and creatinine are all measured and compared to what are considered the normal levels.

Of course, this is just a “Ten Cent Tour” version of the meaning of bloodwork. Your vet has many years of schooling and practice under their belt. They use their knowledge and experience to interpret the subtle chemical interactions represented by your pet’s blood test results. They also combine these test results with the animal’s history, appearance and behavior, and possibly even other tests like X-Rays and urinalysis, in order to diagnose your pet’s condition. But hopefully, armed with this basic explanation of the components of a blood test, you will be able to more effectively communicate with your vet to obtain the best possible outcome for the pet who’s depending on you.

Don’t hesitate to ask your vet to show you your pet’s blood test results on paper. And make sure they help you understand any of your pet’s blood test results that come through outside the normal ranges. A good vet wants their client to understand their pet’s condition so they can be an effective partner in treating the patient’s condition. They know it’s the pet’s owner who will be responsible for administering meds and tracking changes in the pet’s appearance and behavior once the appointment is over. This is best done with a basic understanding of the underlying mechanisms bloodwork can detect and describe.  So ask questions. Take notes. You’re part of a team dedicated to healing an animal that can’t speak for itself.