Blood work: What it means and why your pet needs it (Part 1: The CBC)

Patty Khuly, DVM
By Patty Khuly, DVM on May 2, 2009
Blood work: What it means and why your pet needs it (Part 1: The CBC)

“You want $99 to test his blood before his dentistry? Seriously? I’m thinking maybe we’ll skip the whole dental thing. The anesthesia freaks me out, anyway.”

That’s not usually how it goes where I work. Clients tend to be more polite, at least. But dentistry is one of those wellness services that suffers in a slumping economy. At our place, it’s clear that, despite their respectful receptiveness, fewer clients are making it back for the actual procedure. About 25% less over this time last year.

Luckily, the expense of the necessary pre-anesthetic blood work is NOT standing in the way of my clients’ dentals. That service is still holding strong––likely because we bundle it with basic annual visits so that nearly every pet gets their blood tested annually. But hospitals who don’t take this step are seeing an even bigger slump in their dental care and other wellness services that require blood work.

And I think I know why: Because pet owners need to be educated to understand the value of what they’re buying. Adding in comprehensive blood work with the annual physical and fecal test (with or without vaccines) adds REAL value to a pet’s healthcare regimen. Nonetheless, its PERCEIVED value is negligible unless an owner is informed of how incredibly useful this information can be. 

In other words, pet owners like you will NOT buy blood work (and, most importantly, your pets won't get it) if you have no idea what it’s all about. Here’s a short list of common misperceptions I encounter on this front: 

1. Some pet owners assume that blood work for their pet means the heartworm test only. 

They sometimes arrive at my hospital fresh from elsewhere informing me that we don’t need to draw their pet’s blood because it was just done a month or two earlier. The faxed-over records indicate a heartworm test every year...but nothing more. 

2. Blood work is all the same, everywhere.

A corollary to #1, this common misconception assumes that comprehensive  blood work is the same the world around. In Miami, for example, complete blood work may be different from that in Minnesota, Montreal, London, Tel Aviv or California. (e.g., Here in South Florida, we tend to include heartworm and tick disease tests for dogs; feline leukemia, FIV and heartworm antibody tests for cats.)

3. Evaluating blood work is a procedure that’s acceptably performed every few years. 

Consider that your pet’s lifespan is much shorter than ours. Pets approaching their geriatric years are best served by semi-annual blood work. Pets without major concerns shouldn’t go more than a year without it. Any animal undergoing an anesthetic procedure should ideally have current (within a month) blood work. And sick pets may need it monthly, weekly, daily or hourly, depending on their condition and its severity. 


Beyond the common misperceptions lingers the question of what this all means and why it’s considered so critical. Here’s an explanation:

The most commonly accepted comprehensive “blood work” for pre-anesthetic evaluation includes a minimum of two tests, the “CBC” (stands for “complete blood count”) and “chemistry” (or “chemical panel”). Think of it as one test for the cells in the blood (CBC) and another for the components of the fluid part of the blood (chemistry). 

The CBC (blood cell analysis)

1. Looks at the red blood cells, counts them and takes some measures about how they’re shaped.

It checks the total number of red blood cells and the hemoglobin level (the oxygen carrying molecule in the blood, which is found inside the red blood cells). The red blood cell count and hemoglobin levels tell us whether your pet might be anemic (low red blood cell count, low hemoglobin level) or polycythemic (too many red blood cells, which may indicate dehydration and other disorders) and tells us quite a bit about the health of these cells and what might be happening in your pet’s bone marrow, spleen or kidneys. 

You might also want to know what the "hematocrit" is (also called the PCV or “packed cell volume”). This very commonly mentioned part of the CBC is a measure of the percentage of red blood cells in the total volume of blood. A high hematocrit percentage (over 45%) can indicate dehydration or an absolute excess of red blood cells (polycythemia). A low count usually assists in your diagnosis of anemia.

2. It also counts the total amount of and different kinds of white blood cells.

This paints a picture that explains which kind of white cells are in greatest abundance, along with their total numbers. This is crucial for an investigation of your pet’s infection or inflammation status. We wouldn’t want to do surgery––unless we HAD to––if these cells were elevated or significantly out of whack. 

Neutrophils are the most abundant white blood cell type. When these are elevated we tend to worry about bacterial infections. With viruses, the total white blood cell count is commonly depleted. But these are simplifications. Try not to take them as absolutes. 

3. Finally, it tells us about your pet’s platelets. 

These tiny bits of clotting proteins are crucial. Low platelet levels can be scary when it comes time to stop bleeding. You wouldn’t want your pet to undergo surgery if these were low. Not only could she bleed to death, the low levels of platelets could indicate life-threatening diseases or serious infections (such as those spread by ticks).

4. The CBC may help identify, confirm or support common diseases or disorders.

Here's a brief list of these: 

  • anemia
  • dehydration
  • autoimmune diseases (like autoimmune hemolytic anemia)
  • blood cancers (certain lymphomas, for example)
  • kidney disease (as with chronic renal failure)
  • tick-borne diseases (like Ehrlichia or Lyme)
  • bacterial infections
  • viral infections (like Parvo or Panleukopenia)
  • bone marrow diseases 
  • parasitic diseases (like hemobartonella in cats)
  • poisoning (Tylenol or onion toxicity, for example) 

Here's a cool pic outlining these above components:

blood cells


Tomorrow we tackle the “chemistry” test. Get ready for more fun stuff.

Patty Khuly, DVM


Patty Khuly, DVM


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