Everything You Need to Know About Blood Work From a Veterinarian

Doing blood work is never a waste, even when it results in good news.

A complete blood count tells vets about a pet’s red blood cells, white blood cells and platelets. By: Adina Voicu

“Blood work, shmud work! Why is my vet always asking me to do blood tests?”

I hear this complaint — or a reluctance to pay for blood tests — frequently. Veterinarians often defend themselves about recommending blood work. “Why do you have to do blood work?” asks the human of an 8-year-old Cocker that needs dental work. “What will it tell you?” complains the human of a 4-year-old cat who has not been eating for several days. “Just take off the lump without the blood work,” says the price-shopping person with a young dog with a skin tumor.

Basic blood work — a complete blood count (CBC) and a chemistry profile — are completely noninvasive tests that tell us a great deal about the general health of your pet, young or old, sick or healthy. Vets are so happy we can do highly reliable blood work in a matter of minutes rather than days and at a reasonable cost. If clients really understood how much a CBC and a chemistry can tell us, I think they’d show less reluctance.



In a CBC, a very small amount of your pet’s blood is taken from a vein and placed in a lavender-top tube. The blood draw takes about 10 seconds. The CBC informs us about red blood cells, white blood cells and platelets.

Red Blood Cells

If the red cell count (hematocrit or PCV) is low, your pet is anemic. Then your vet has to find out why your pet is anemic.

If the red cell count is high, your pet is most likely dehydrated. Rarely a high red blood cell count suggests a disease called polycythemia.

Are the red blood cells healthy? A simple CBC tells us much about your pet’s actual red blood cells, which is like a window into your pet’s bone marrow, spleen and kidneys.

White Blood Cells

There are a number of different white blood cells in your pet’s peripheral blood. The kind of white cells and the relative numbers of these cells help your vet decide whether your pet might be suffering from an infection, bacterial or viral, inflammation or cancer.

Although the white cell count does not give us specifics about where an infection might be, where the inflammation is coming from or if your pet actually has cancer, it can lead us in a specific diagnostic direction.


Platelets are proteins that help pets make a blood clot. A low platelet count is a worry and should be addressed, particularly prior to any surgery whatsoever.

The vet takes your pet’s health seriously — hence the blood work. By: hzv_westfalen_de

The Chemistry Profile (or Panel)

Once we’ve learned how your pet’s blood cells are doing with a CBC, we turn to your pet’s serum, the fluid in your pet’s blood. This blood is taken in that same 10-second blood draw as the CBC and placed in a second red-top tube. We don’t need much of your pet’s blood to do a battery of tests.

Many enzymes and elements are found in the serum that tell us tons about your pet’s organs, metabolic state and electrolyte status.

Liver, Kidneys, Gallbladder

While the basic chemistry panel can’t give us specific answers as to what liver disease, gallbladder condition or kidney disease your pet might be suffering from, increases in specific enzymes are red flags and tell us we need to look deeper or monitor certain organs. The chemistry allows us, for example, to pick up early (or advanced) kidney disease, injury to the liver or possible gallbladder problems.


Alterations in electrolytes like sodium, potassium and chloride are serious. They can:

  • Signal endocrine diseases, like Addison’s
  • Help us measure dehydration
  • Aid in what kind of IV fluid supplementation your animal needs if there has been vomiting, diarrhea, kidney disease or other illness
  • Help us complete a medical picture in a pet with diabetes, GI, pancreatic, kidney or endocrine disease

Blood Glucose

An elevated blood glucose (blood sugar) suggests diabetes. A low blood sugar indicates other syndromes such as insulinoma, starvation or hypoglycemia of young puppies.

Misconceptions About Blood Tests

The Heartworm Test

The annual heartworm test or 4dX test for dogs does not include other blood work. The test determines if there is evidence of heartworm or other tick-borne diseases. Your vet must specify that she’d like to do a CBC/chem or “blood panel” or “comprehensive blood work” to look for things beyond the heartworm test.

Limitations of Blood Tests

Blood tests give important diagnostic information, not necessarily a diagnosis. The diagnosis, however, cannot ultimately be made without the blood tests.

“Will the blood test tell us if he has cancer?” is an all-too-frequent question. The CBC/chemistry panel does not diagnose cancer. If the pet is anemic, shows atypical cells in the CBC, has high liver enzymes, etc., it can point us in a certain diagnostic direction or help us flush out the overall picture.

Blood Work Has a Shelf Life

Blood work must be repeated if your pet’s health status is changing or if we are staging or tracking a chronic disease.

If a pet has recently lost a lot of weight or has begun to drink a lot of water, I will definitely recommend blood work. The client might say, “But they had blood work done 6 months ago and it was fine.” Clearly, the pet’s health status has changed if they have lost significant weight, or if thirst or appetite have changed dramatically. The blood work should be repeated.

If we have diagnosed a chronic problem, like kidney, liver or diabetes, serial blood work is one of the best ways to monitor improvement or exacerbation of disease.

Basic Blood Work Costs

Most CBC/chemistry panel combinations run somewhere between $100 and $200. They may be more expensive in certain regions of the country or in emergency situations.

There are many, many other blood tests and “comprehensive panels” that include other tests. Obviously, these tests carry an additional price tag. A retroviral panel, for example, will include Felv/FIV/FIP for a sick kitty. Thyroid testing is very common in both dogs and cats. There should be no confusion about these costs if your vet is communicating clearly.

When Basic Blood Work Should Be Done

These simple tests give us so much information with no trauma to your pet and at a reasonable cost. They are recommended frequently:

  • As part of a wellness exam, for baseline lab values, particularly as your pet ages
  • Prior to most anesthetic procedures
  • When your pet is ill and we are searching for a diagnosis
  • To monitor existing conditions such as kidney disease, liver disease or diabetes
  • Prior to starting a new medication
  • If your pet is taking certain medications in the long term, such as NSAIDS, steroids or chemotherapy drugs

Because our pets have shorter life spans compared to humans, the basic CBC/chemistry is considered by many as part of a pet’s annual physical. “Middle age” for some pets can begin at 5 years old.

Insurance plans often cover these blood tests as part of a wellness exam. Curious about the cost of pet health insurance? It’s more affordable than you probably think. Get your FREE, no-hassle quote here (affiliate link).

Veterinarians like to give good news. Often, we are able to tell a client their pet’s blood work is normal.

“Then why’d you have to do it?” I’ve heard this over the years from Mrs. Pennypinch or Mr. Distrust. If your doctor called you to tell you your blood work was normal, wouldn’t that be a relief?


This pet health content was written by a veterinarian, Dr. Debora Lichtenberg, VMD. It was last reviewed April 11, 2018.


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