Everything in your dog's body has its 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.
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.
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!
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.
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.
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.
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.
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.
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, 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.
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, 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.
Further reading:
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I have a friend who is going through kidney issues with her dog and I know has struggled to make sense of all these numbers and tests. I'm going to share your post with her. I'm sure it will help. Thanks!
ReplyDeleteA friend's dog has been having kidney issues. He has had multiple tests done. I don't think he has had a GFR done though.
ReplyDelete"...kidney damage won't show up in creatinine levels until 75% of kidney function is lost" Wow I didn't know this! Thanks for educating us with strategies to monitor our pet's health better.
ReplyDeleteThey not really advertise that. The reason for that is, though, that it takes that much of kidney function being lost for them start being unable to do their job. Meaning, there is a lot of built-in redundancy. That's why one can donate kidney and be fine.
DeleteUnfortunately, the creatinine levels don't get elevated until all the redundancy is used up. So not an ideal early screening tool.
The last time I was at the vet they said Layla was really healthy for her age but we did decide that next visit we going to do blood tests to make sure all is good especially as she is 11 years old. Great post as always
ReplyDeleteYes, I'd absolutely run blood test at least once a year.
DeleteHarvey has kidney issues. The vet cheerfully told me he has 20% kidney function when he went for his check up. Fine. That aside he is doing OK so far.
ReplyDeleteI am guessing there are cat tests too?
It seems the tests are the same for kitties as for dogs.
DeleteThis may sound stupid, but I didn't realize dogs need to be carefully monitored for kidney disease as well as cats. I'm lucky my girls have been very healthy.
ReplyDeleteI'm glad your kitties are doing well. Anybody, who has kidneys can suffer from kidney disease.
DeleteSuch important information and written in a very easy and helpful way. I'm quite familiar with BUN and creatinine levels having had a dog who was on Canine Epilepsy meds, and checking his levels every 5 to 6 months to keep an eye on his liver was key. I so agree that while the initial reaction is slight panic, it does always seem that something is a bit out of whack on the blood panels. I'd study those blood test results from top to bottom, just starting to sigh, then would get hung up on a high level. I'm Pinning to share this very informative post.
ReplyDeleteKidney failure is actually something I worry about with my dogs. I know it's such a common issue in pets. Thanks for this detail.
ReplyDeleteLove & biscuits,
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My girls get annual blood work done as part of their Wellness plan. It's even more important now to have urinalysis tests done on both cats since Truffle had surgery to remove bladder stones earlier this year.
ReplyDelete