Food For Thought: Labs

Lab work can tell a great deal about what’s going on with your cat’s or dog’s body. It’s not difficult to imagine that labs are essential to determine how well a diet is working. We rely on this kind of data to fine-tune diets so we can achieve the desired nutritional outcomes.

Lab results are often several pages of abbreviations, terms, and numbers. That’s already a lot to process—but there’s even more to consider.

Some lab tests are straightforward, providing a simple “yes” or “no” answer. For instance, a test may show whether your cat is positive for Feline Immunodeficiency Virus (FIV) or heartworm. 

Most other tests, however, are reported as numbers or values. Laboratory test results reported as numbers are not meaningful by themselves. Their meaning comes from comparison to reference values. Reference values are the values expected for a healthy animal. They are sometimes called “normal” values and are associated with a normal range.  The lab values from your baby either fall within the ‘normal’ range, are above the range (a high result), or fall below the range (a low result).

To determine ranges—and what’s considered ‘normal’—labs may conduct their own studies for the tests they perform, they may adopt reference ranges from test manufacturers or other labs, or they may derive reference ranges from existing patient data.

Lab-to-lab variability can result from differences in equipment, reagents, and analysis methods. As a result, there is often no single universal reference value. Consequently, for most lab tests, there is no universally applicable reference value.  Comparing a lab result from lab A, to the same test from lab B, may show a different value.

Reference ranges are usually based on “typical” pets—those fed commercial kibble or canned diets, which are generally lower in protein. In contrast, raw diets with whole, fresh ingredients are higher in protein, but only about 5% of dogs and cats are fed this way. That means most lab ranges are built on values from pets with very different diets.

For example, creatinine is produced as a natural byproduct of muscle activity and is removed from the blood by the kidneys. Creatinine is often measured as a gauge of how well the kidneys are functioning. Creatinine levels are affected by an animal’s muscle mass. Because males have greater muscle mass than females, younger animals have more muscle mass than aged animals, the reference values can vary.

Lab results are also affected by timing and stress. The amount of time since the last meal, or the stress of a car ride and vet visit, can alter chemical levels in the blood. These influences may cause temporary fluctuations outside the “normal” range without indicating true disease.

Feeding a raw, high-protein diet can naturally elevate certain lab values. For example, creatinine and Blood Urea Nitrogen (BUN) often run higher in animals on protein-rich diets. A slightly elevated result due to protein metabolism doesn’t necessarily mean kidney disease—but interpretation should always be left to your veterinarian.

There is a lot to consider when reviewing lab results. Your veterinarian is your partner in interpreting them, but understanding the factors that influence values allows you to ask better questions. Outliers should not be viewed as absolutes.

Ultimately, you are responsible for making health decisions for your pet. The more complete your understanding of lab results, the more informed and confident your choices will be.