Myth #12: "'Normal' Lab Tests Are Always Normal"
The Truth:
“In Normal Range” Depends On Your Cat
Interpretation of feline lab tests is more involved than simply “normal” versus “abnormal.”
Cats love to ignore laboratory “normal ranges.” (And veterinary textbooks, too.) Individual cats often have their own “normals”: levels of this or that, out of the population normal range, but perfectly normal for them. Knowing your cat’s own “normal” lab tests can be critical to proper interpretation if your cat becomes ill.
Some “abnormal” cat lab tests are a result of stress, not illness. For example, a cat’s blood glucose can shoot up to nearly 4 times the normal level, just from the stress of drawing blood. This feline-only phenomenon often leads to a misdiagnosis of diabetes.
Population normal ranges can be uselessly large. At one major veterinary lab, the normal range for feline white blood cell counts is between 3,900 and 19,000. Let’s say your cat becomes ill, and testing shows a white cell count of 18,000. If her normal level is 4,000, that’s a big deal. If her normal is 17,000 – not so much. Interpretation of that 18,000 is completely different based on your cat’s individual normal level.
Population normals are influenced by nutrition. Let’s face it. Dry cat food is bad for cats, but it’s what most people feed. It contains far less muscle meat than cats should eat. This has created an artificially low “population normal” for some kidney lab tests. Creatinine, for instance, is often “above normal range” in cats fed a carnivore-appropriate diet. This is commonly mistaken for kidney failure unless evaluated in concert with other lab tests and a good dietary history.
Feline veterinarians are skilled in accurate interpretation of cat lab test results. Lab tests are only as good as their interpretation. Your cat deserves the best!