Understanding your pet’s lab tests

understanding your pet's lab tests

Lab tests are an important part of your dog or cat’s routine checkups. We take a close-up look at some of the most common blood tests, and what they can tell you about your best friend’s health.

1. BUN/Creatinine/SDMA

  • BUN (blood urea nitrogen) is one of three blood tests for kidney function. It is a good screening test but not perfect, since 60% to 70% of kidney function has to be destroyed before it elevates significantly. BUN is also affected by diet, exercise and muscle mass, so results can be skewed due to factors unrelated to the kidneys.
  • Creatinine refers to an amino acid constituent of muscle protein. Like BUN, this test also doesn’t show a significant elevation unless 60% to 70% of kidney function is gone, and it can also be affected by diet, exercise and muscle mass (but not as much as BUN). Blood profiles that incorporate only these two tests can accurately diagnose kidney disease once it has progressed to a later stage, but they are not so good for diagnosing very early disease.
  • This is why a third test called SDMA (symmetric dimethylarginine), which tests for the amino acid arginine, is recommended. SDMA levels elevate very early in the course of kidney disease — anywhere from 12 to 36 months before BUN and creatinine levels elevate – reflecting only 25% of kidney damage versus 60% to 70%. From a functional medicine perspective, adding the SDMA test to the blood profile is extremely beneficial as we can diagnose kidney disease at a very early stage (Note: many veterinarians do not routinely test for SDMA.)
  • Other tests that can help diagnose pets with kidney failure include blood levels of phosphorus and calcium. Phosphorus in particular reveals the severity of kidney issues because it elevates when the kidneys are seriously damaged. Pets with elevated blood phosphorus levels and elevated levels of the kidney enzymes mentioned above are much harder to treat and have a poorer prognosis.


ALT stands for alanine aminotransferase, and ALP (also called SAP) for alkaline phosphatase. These two tests are useful for diagnosing problems of the liver, gallbladder and adrenal glands. ALT increases whenever there is any damage or insult to the liver or gallbladder. Unfortunately, while ALT is a good test, it cannot tell us why the liver is damaged; other tests such as radiographs, ultrasound, and liver biopsy are needed to reveal the cause of ALT increases.

ALP can also increase when the liver or gallbladder are damaged; however, ALP most commonly increases when the adrenal glands are diseased, increasing their hormonal output, usually of cortisol. Pets with ALP increases have adrenal disease that may progress to Cushing’s, a severe adrenal condition that at times requires chemotherapy (in addition to natural therapies) to be correctly treated.

Sadly, I see many pets who have been misdiagnosed with liver disease based on increased blood levels of the ALP enzyme. These pets really have adrenal disease and must be treated correctly. Treating them for liver disease (including doing surgery for a liver biopsy) can further injure or even kill them.

3. T4/FT4

Because thyroid disease is so common in dogs, checking both Total T4 (TT4) and Free T4 (FT4) values is essential. Because hormonal testing costs more than a simple chemistry profile, many doctors leave these tests out (or only include the less accurate T4 test). When this happens, it poses a potential problem to the pet because thyroid disease can be overlooked.

Because thyroid disease resembles other conditions in clinical signs, I believe it’s always valuable to include thyroid testing for every pet.

Considering pet insurance

If your dog or cat appears healthy, consider getting pet insurance before his next checkup. In my practice, over 50% of the pets we test using the lab tests outlined in this article show abnormal findings — which are covered by pet insurance once the abnormality is noted. Don’t wait until a problem arises and then try to insure your pet. Play the odds that some test will come back abnormal at some point, and get coverage before problems arise. It will save you money in the long run.

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Veterinarian Dr. Shawn Messonnier wrote The Natural Health Bible for Dogs and Cats, The Natural Vet's Guide to Preventing and Treating Cancer in Dogs, and 8 Weeks to a Healthy Dog. He's the pet care expert for Martha Stewart Living's "Dr. Shawn — The Natural Vet" on Sirius Satellite Radio, and creator of Dr. Shawn's Pet Organics. His practice, Paws & Claws Animal Hospital (petcarenaturally.com), is in Plano, Texas.