What does my pet's blood test show?

A routine blood test is two tests on one sample. The blood count looks at the red cells, the white cells and the platelets, and the chemistry panel measures chemicals that show how the kidneys and the liver are working and how high the blood sugar is. A number outside the printed range is a reason to look further, not an answer by itself: up to 5 in 100 healthy animals have one on any single test.

In short

The blood count covers red cells, white cells and platelets. The chemistry panel covers the kidneys, the liver, blood sugar, proteins and salts.
Ask the clinic whether your pet should skip a meal first. Fat in the blood after a meal can spoil the sample.
The American Animal Hospital Association asks for blood work once a year for a healthy mature adult dog, and every 6 to 12 months for senior dogs and cats.
Keep every result. A change from your pet's own earlier numbers can show a problem before a number leaves the range.

What is in a routine blood test?

The Merck Veterinary Manual's pages for owners describe both parts. The blood count is written CBC on the bill. The table shows what the manual says a high or low value can go with.

On the result sheet	What it is	What a high or low value can go with
Packed cell volume, PCV	The share of the blood that is red cells.	High with dehydration. Low suggests anemia or bleeding.
White blood cells	Several types of cell.	They rise with inflammation, infection, short-term stress, allergies and some cancers.
Platelets	Particles that help blood clot.	They rise with injury and can drop with immune, clotting or bone marrow problems.
Urea, also written BUN	A waste product the kidneys clear.	High with low blood volume, kidney failure or bleeding in the gut.
Creatinine	Another waste product the kidneys clear.	High with kidney disease, a blocked urinary tract or a ruptured bladder.
Glucose	Blood sugar.	High with diabetes or stress. Low with hormone problems or starvation.
ALT and ALP	Two enzymes listed with the liver values.	High with liver damage, muscle damage or an overactive thyroid.

A panel can also include proteins, salts such as sodium and potassium, thyroid hormones, and markers for the heart and the pancreas.

For the kidneys there is one more value, SDMA. Cornell's Feline Health Center says creatinine generally does not rise in a cat until almost 75 percent of kidney function is lost, while a rise in SDMA can be detected when about 40 percent is lost. It says the vet will ideally judge kidney function on at least two blood and urine samples taken within two weeks of each other. What the urine adds is on Why does the vet want a urine sample?

Does my pet need to fast before a blood test?

Ask when you book, because the answer depends on the tests being run. The reason for fasting is fat. Cornell University's clinical pathology site says fat in a blood sample usually comes from taking blood from an animal that has eaten, and that a fast of at least 12 hours keeps it to a minimum. The Merck manual adds that blood sugar rises with stress or excitement, including the stress of being handled for the sample.

How often should blood be tested?

Animal	What the guideline says
Young adult dogs	Consider one set of tests as a baseline.
Mature adult dogs	Once a year.
Senior dogs	Every 6 to 12 months.
Cats aged 1 to 6	Consider a single baseline, then test as needed.
Cats aged 7 to 10	Recommended, every one to two years.
Cats over 10	Strongly recommended, at least once a year and preferably every six months.

The dog rows are from the American Animal Hospital Association's 2019 life stage guideline, and the cat rows from the 2021 guideline it wrote with the feline practitioners. Both guidelines are written for animals that appear healthy and do not cover blood work before an anesthetic, which is on What every line on a vet bill means. The American Veterinary Medical Association says senior pets need to see a vet twice a year or more, and that the visit may include blood work.

What can a blood test tell me, and what can it not?

Up to 5%of healthy animals fall outside the normal range on any one test (Cornell University).46%is the chance that a healthy animal has at least one slightly odd result when 12 tests are run (Cornell University).

The range printed next to each result is built from healthy animals. Cornell explains that a laboratory tests a large group of healthy adults of one species, ideally at least 120, and takes the middle 95 percent of their results as the range. So up to 5 percent of healthy animals land outside it on any single test, and the more tests are run, the more likely it is that one comes back slightly off.

"One test is very seldom specific to one clinical condition" Merck Veterinary Manual, Clinical biochemistry, updated August 2026.

So the vet reads the numbers as a pattern, together with the exam and what you have seen at home.

Ranges differ from one laboratory to another. Cornell says changes over time can only be judged when the same laboratory and method are used.
Your pet's own earlier results are the best yardstick. The animal hospital association says some diseases are found from a rise over earlier results, before the number leaves the normal range.
Nobody has measured how often an odd result in a healthy-looking dog turns out to be disease. The association's dog guideline says studies have found something abnormal in 6 to 80 percent of dogs tested at routine visits or before an anesthetic, and that no study followed the dogs up.

When is a blood test not worth the money?

Routine blood work on a healthy pet is a search for problems that are not showing yet. The dog guideline calls its schedule the opinion of its task force, and the cat guideline says specific data documenting the benefits are not available.

A young adult has no yearly schedule in the guidelines. The advice is to consider one baseline test.
A smaller panel may be enough. In the association's article for cat owners, a vet says that for clients on a budget she may run a smaller panel each year and the larger one every other year.
The guidelines had company support. The association's pages say they were supported by companies that include a maker of laboratory tests, so it is reasonable to ask what a result would change for your pet.

The figures Petipedia could source for vet prices are on What does a vet bill cost? The national averages for a blood count and a chemistry panel are in the cost table on When is my pet a senior, and what should the checkup include?

What should make me call the vet without waiting for the next test?

Cornell's Feline Health Center says cats in the early stages of kidney disease very commonly show no obvious signs, and that later they may urinate more, drink more, eat less, lose weight and seem tired. A change like that is a reason to book a visit now. What counts as drinking too much is on How much should a dog or cat drink?

What to ask the vet

Should my pet skip a meal before the blood is taken, and does that change for a puppy, a kitten or a pet on insulin?
Which tests are in this panel, and is there a smaller one that would answer the question?
Is this result outside the range by a little or by a lot?
How does it compare with my pet's last results, and may I have a copy to keep?

Sources

Sources read on 2 October 2026; every number is as the source gives it.