Canine Kidney Function Screening: Checking Your Dog’s Kidney Function

Everything in your dog’s body has a distinct job. The kidneys perform several vital tasks, including filtration of waste and toxins and essential regulatory functions.

Kidney function is assessed based on values that reflect how the kidneys are able to do their job.

Canine Kidney Function Screening: Screening Your Dog's Kidney Function

Measuring blood levels of nitrogenous wastes and compounds (azotemia)

The two familiar values that belong in this group are blood urea nitrogen (BUN) and creatinine. These are a product of bodily processes, and it is the kidney’s job to get rid of them.

BUN is a byproduct of protein breakdown, but its reliability to asses kidney function is questionable. Kidney dysfunction can increase BUN levels in the blood but so can some other things. When looking at any abnormal blood results, it is always important to consider the big picture, and the contribution of BUN is not as telling as it was hoped to be in the past.

Blood urea concentrations are more influenced by factors that have nothing to do with kidney function than creatinine. BUN may increase due to a high protein diet, after a meal or if there is bleeding in the GIT.

Creatinine is the waste product of energy consumption in the muscles. How much creatinine there will be in a healthy dog’s blood, then, depends on their muscle mass.

Creatinine is more specific in reflecting the kidney’s filtering ability but it can also get elevated due to dehydration, severe heart disease, urinary obstruction … even some medications can mess with BUN and creatinine levels.

BUN: creatinine ratio is also measured, but even a high-protein diet can influence any results.

The biggest problem with evaluating kidney function based on creatinine levels

This is pretty important. All else aside, kidney damage won’t show up in creatinine levels until 75% of kidney function is lost! That’s a lot of damage before anybody has a clue!

Important note

The big picture is more important than any one value. When one of Cookie’s blood tests came back with high BUN and creatinine levels, I could easily have panicked. I kind of did a little bit. But over time I also learned that many blood panels come back with one or two odd values out of whack, and it doesn’t have to mean anything per se other than, for example, that Cookie would have been dehydrated at the time.

We followed up with testing urine concentration, and it was good. We later ran a new blood panel, and it was fine as well.

Values versus trends

If a blood test shows values within a normal range, is that all that is important? Particularly with something such as creatinine which doesn’t get high until much of kidney function is already gone?

What if it tests within range but climbing a bit each time? Such progression is important to note. For Cookie, I keep a trends chart for each of the main values. Here is an example of Cookie’s progression of creatinine levels.

29 – 135
44 – 133
27 – 124
27 – 124
27 – 124
44 – 133
27 – 124
44 – 141
44 – 133
27 – 124
27 – 124

You can figure I am pleased with that progression. Note the renegade value and see that different labs have different normal ranges.It is critically important to never run with urea and creatinine results without confirming whether there is a problem by testing urine specific gravity ((see below)

There are other things that are measured on a comprehensive blood panel which can contribute to the bigger picture. Poor kidney function can also show as changes in electrolyte levels or anemia. Dogs with kidney disease also may have high blood pressure.

The crucial test to evaluate kidney function is urinalysis.

I listed the blood results that might point to kidney problems first because you are likely to see o hear about these first. If you’re taking your dog for a wellness exam, you might remember to bring a stool sample but how many of you bring in a urine sample as well? Yet, the main indicator of kidney function is found in the urine–the specific gravity of urine. This value reflects the kidney’s ability to concentrate urine. It is best to test first morning urine (freshness isn’t important in this case). During the day the urine concentration can fluctuate greatly. In dogs, a specific gravity of 1.030 or greater indicates adequate urine concentration.

One tricky part is that urine concentration can be low both from impaired kidneys or something else going on in the body that interferes with the kidneys being able to do their job properly.

Looking at the presence of protein in the urine can be helpful; persistent findings of protein in urine can point to kidney disease. That’s why, again, the big picture is what you ought to seek.

Enter SDMA

Given how far the kidneys have to be gone for the standard lab tests to show there is a problem, scientists have been continually trying to find better indicators of kidney function.

SDMA is a relatively new test, looking not at levels of waste compounds but a specific biomarker that reflects filtration rate instead. It is touted to be able to detect kidney function loss at 25% rather than 75% like with measuring creatinine. That means knowing the kidneys have a problem 17 months earlier when most of their function is still intact.

It is also a value that is less affected by things that go on in the body that are unrelated to kidney health and function.

Too good to be true? I don’t know. Some of the veterinary experts I respect and admire seem to be quite excited about it. Either way, I have added SDMA to the values I want to see on Cookie’s routine blood panels.

Glomerular filtration rate (GFR)

This a highly reliable, fancy test the lights of which you’re not likely to see unless you work with a specialist. It involves the introduction of a compound for the kidneys to filter and then measuring how it cleared. Fancy and complicated but useful in complicated cases when other testing fails to provide answers.

Related articles:
SDMA Kidney Function Test: Veterinarian Share Opinions and Experience With The New Way Of Monitoring Kidney Health In Dogs

Further reading:
Laboratory evaluation of kidney disease

Categories: Blood workDiagnosesDog health advocacyInterpreting lab resultsKidney functionSDMAUrinalysis

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Jana Rade edited by Dr. Joanna Paul BSc BVSc

I am a graphic designer, dog health advocate, writer, and author. Jasmine, the Rottweiler of my life, was the largest female from her litter. We thought we were getting a healthy dog. Getting a puppy from a backyard breeder was our first mistake. Countless veterinary visits without a diagnosis or useful treatment later, I realized that I had to take Jasmine's health care in my own hands. I learned the hard way that merely seeing a vet is not always enough. There is more to finding a good vet than finding the closest clinic down the street. And, sadly, there is more to advocating for your dog's health than visiting a veterinarian. It should be enough, but it often is not. With Jasmine, it took five years to get a diagnosis. Unfortunately, other problems had snowballed for that in the meantime. Jasmine's health challenges became a crash course in understanding dog health issues and how to go about getting a proper diagnosis and treatment. I had to learn, and I had to learn fast. Helping others through my challenges and experience has become my mission and Jasmine's legacy. I now try to help people how to recognize and understand signs of illness in their dogs, how to work with their veterinarian, and when to seek a second opinion. My goal is to save others the steep curve of having to learn things the hard way as I did. That is the mission behind my blog and behind my writing. That is why I wrote Symptoms to Watch for in Your Dog, which has turned out being an award-winning guide to dog owners. What I'm trying to share encompasses 20 years of experience. Dr. Joanna Paul BSc BVSc is our wonderful sponsor and has been kind to edit and fact-check my important articles.

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