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.

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.

Date	Lab	Creatinine	Normals
8/23/2013	IDEXX	112	29 – 135
3/6/2014	IDEXX	107	44 – 133
10/23/2014	Walden	87	27 – 124
1/14/2015	Walden	97	27 – 124
5/15/2015	Walden	141	27 – 124
10/16/2015	IDEXX	96	44 – 133
3/15/2016	Vetscan	98	27 – 124
3/18/2016	Antech	90	44 – 141
12/22/2016	IDEXX	86	44 – 133
8/23/2017	Walden	82	27 – 124
5/23/2018	Walden	89	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.

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