Vet Test Results Demystified

This is week’s Q & A question for our cat expert Dr. Richard Goldstein. have a question for him? Email it to [email protected].

Q: Can you please explain or demystify blood panels? It’s all Greek to me. When something is marked high, should I be worried? My vet wasn’t that alarmed about these elevated results: BUN/Creatinine ratio (39), CPK (721), triglycerides (1397) with regards to an older male cat. All his other tests are in normal range. I’m worried about kidney disease and wonder what I can do to prevent it.

A: Blood panels are an invaluable source of information into the inner workings of the body. But, by themselves, test results do not offer all the answers. They must be interpreted in combination with physical examination findings and any symptoms the cat is showing. Individual test results on a chemistry panel can often point to several possible interpretations, not just one. And there’s not any one test that will definitively point to one disease or another. If changes are detected, it’s important to analyze their significance.

Case in point: the BUN (blood urea nitrogen), and creatinine are typically thought of as the “kidney enzymes”. However, BUN and creatinine can also elevate when a pet is dehydrated, or has a lower urinary tract obstruction, or Addison’s disease. How do you tell the difference? The physical exam, clinical symptoms, and other lab results must be interpreted together. It’s like fitting together the pieces of a puzzle. If we’re concerned that changes in the blood work may indicate a kidney problem, then a urinalysis is in order first, to look at the concentrating ability and functionality of the kidneys.
Another point to keep in mind is that “normal” values are averages, based on thousands of samples. But, as we know, with averages, someone has to be above, and someone has to be below those numbers. That doesn’t necessarily mean they’re “abnormal.” In fact, one study suggested that on an average blood panel, a “normal” patient could be “out of range” on at least 10% of the tests! And “normal ranges” can even vary between laboratories. That means it’s even MORE important to interpret the significance of out-of-range values.

Since there are a variety of ways to interpret lab results, it’s vitally important for you to have a frank discussion with your vet. Talk about the results and what the significance may or may not be based on your cat’s physical exam and home habits. Ask questions.

I am a big proponent of annual or semiannual wellness blood screening for cats, especially as they age. Cats are amazing at hiding symptoms of disease until they are really sick. Following their blood values and physical exam findings over time can help us catch problems early so that we can intervene.

Here’s an example: Fluffy is a 9-year-old male cat. Last year, he weighed 11 lbs, and had a normal physical exam. His BUN was 20 (let’s say this lab’s normal range is 15-30), and his creatinine was 1.0 (0.8-2.4 is normal for this lab). This year, Fluffy weighs 10.5 lbs. His physical exam is still normal, and he is still acting normally at home. His BUN is now 27, and his creatinine is now 1.8. These values are still within the “normal range”, but they are trending upwards. If we just checked this year’s sample, and didn’t have last year’s results to compare to, we might not think anything of those numbers. But compared to last year, they have increased, and his weight has dropped a bit. This may warrant further investigation or monitoring. Make sense?

As far as your specific blood test questions, the BUN/Creatinine ratio is just a calculated number. Sometimes it can be used to help differentiate between dehydration and kidney-related elevations in BUN and/or creatinine. It’s significance, however, is questionable. CPK is a “muscle enzyme” and can sometimes falsely elevate when the blood is drawn into the syringe, or it can elevate when there is cardiac muscle disease. Triglycerides are fats in the blood, and can elevate after a meal, or when there are digestive problems.

As you can see, by themselves, individual test values aren’t much help, and must be interpreted as part of the entire picture. The “art” of medicine is being able to take all those individual brush strokes and create the painting. Speak to the artist and ask him what he sees.

Editors Note: When receiving test results for pets or humans for that matter, a little knowledge can be a dangerous thing. With the advent of Google searches, it’s easy to get confused or misled. I’ll reiterate what Dr. G. said: ask questions. Don’t be embarrassed if you don’t understand. A good vet or doctor will take the time to explain.