Kidney Failure A New Test

Is Your Cat Trying To Get Your Attention?

Check Out This New Test.

 

Cat getting your attention

Hello and thank you for taking the time to look at this page.

Since qualifying as a vet in 1990 I have been extremely frustrated by our lack of ability to diagnose kidney problems early on in the course of the disease. Prior to this new test being launched our older diagnostic tests would only detect kidney disease once 65 to 75% of kidney function had already been lost which I’m sure you will agree is far later than ideal.

I’m very excited to be able to tell you about a new diagnostic test for chronic kidney disease that has been introduced into the UK from America. I personally think that this test has so much to offer cat owners like yourselves because it has the capability of revolutionising our ability to DIAGNOSE KIDNEY DISEASE SO MUCH EARLIER and therefore manage and treat the problem sooner. This new test will I feel SAVE the lives of many cats and will transform the way we go about managing this very common problem.

 Below is a video which talks you through the contents of this page.

Major functions of the kidneys

  1. Excretion of waste or toxic products– they excrete waste or toxic products from the body which have been produced by the metabolism of proteins. So when the kidneys fail these toxic products tend to accumulate in the body.
  2. Maintenance of water and electrolyte balance- Secondly they are responsible for the maintenance of water and electrolyte balance so this effectively maintains our hydration status and keeps our salts such as sodium, potassium, calcium and phosphates at the correct levels. Cats with kidney failure will often have too low levels of potassium which can make their muscles weak and they therefore require potassium supplementation and too much phosphate in the blood which can lead to a calcium being removed from their bones making their bones weak.
  3. Production of the hormone Erythropoietin– the kidneys are also responsible for producing a hormone called erythropoietin which stimulates the production of red blood cells, so cats with kidney failure are generally anaemic and occasionally this anaemia can become life-threatening.

How common is kidney disease?

So just how common is CKD and this is indeed a very good question? We know it’s a common problem we know it tends to increase with the age of the patient but just how common is it?

Now the illustration below is very interesting.

Frequency of kidney disease in cats and dogs

On the left we have the prevalence as detected by azotaemia or the old diagnostic technique and on the right we have a paper which was published fairly recently in the Journal of Feline Medicine and Surgery. Now, this is an American study that was prepared by vets at North Carolina State University who were performing an investigation into degenerative joint disease. They performed some additional diagnostic tests to assess the incidence of chronic kidney disease in cats in various age groups as illustrated in the graph. Now the incidence of chronic kidney disease CKD in the older cats the 10-14.9 and the 15-20 groups was around that which I would have expected. I was however, SHOCKED to see the values they reported in the younger kitties the 0-4.9 and 5-9.9 their results seemed quite a lot higher than I expected.  Having said that if I look at the situation here at Lawns with the staff’s pets, we have six cats between us that are under 10 years old, two of whom have CKD and one of those is sadly quite serious. So it’s certainly a problem in young cats but whether or not it’s quite as prevalent as suggested here is as yet unknown to me BUT hopefully this new test will be able to shed some light on the situation.

How was kidney disease diagnosed?

Historically as a profession we have performed blood tests to measure BUN or toxic products from protein metabolism and creatinine levels and we look at your pet’s urine to see how concentrated it was and check for proteins in the urine, we could also measure microalbuminuria urine which increased in certain types of kidney disease. Unfortunately all these tests are relatively insensitive and don’t show changes until quite late in the disease process. Now the gold standard was measuring something called GFR which is very accurate but for technical reasons is not a test which can be performed in clinical practice.

Graph depicting the historic diagnosis of kidney disease

Here we are illustrating time along the axis at the bottom and we’ve got kidney damage occurring at the point marked and that’s measured by the redline deteriorating with time. The yellow line at the top which measures what’s going on in the urine, and is looking at specific gravity or how concentrated the urine is, we see that it continues as normal often for quite a while after the damage occurred and then starts to decline. The blue line represents the old blood test we used to use and we can see the toxins, the urea BUN and the creatinine. After the kidney damage occurs this carries on horizontally for quite a long time until it rises at the end. We used to make a diagnosis using the old tests quite a long time after the original kidney problem started and that therefore a lot of kidney function has already been lost before we started managing the problem.

Infographic showing creatinine demonstrating kidney failure when 75% of kidney function has been lost

New SDMA Diagnostic Test

So, let’s look at the new kidney function test and this is involves measuring a substance called SDMA or symmetric dimethyl arginine. There are three key attributes which makes this particular useful; it’s a biomarker for kidney function, it reacts earlier than creatinine and it is specific for kidney function

Infographic 3 key attributes of SDMA

So what is SDMA. Essentially SDMA is formed in cells when arginine which is an amino acid and a constituent of certain proteins in cells is metabolised whereupon it then goes to the kidneys and is excreted.

Infographic showing how SDMA if formed and excreted

If we remember back to the old test when we measured creatinine, at which point we were only really picking it up once 75% of kidney function had been lost which obviously wasn’t very good.

Photo depicting that SDMA isn't impacted by lean muscle mass

In addition SDMA unlike creatinine is not affected by the size of the patient, so for example in these pictures here the dogs and cats in the top pictures are relatively well muscled so they would have higher blood creatinine values than the poorly muscled pets in the bottom pictures, even if their kidney function were the same which makes the interpretation of creatinine blood tests more challenging.

So, with the SDMA we are going to get an earlier diagnosis when on average only 40% function has been lost and we may pick some cases up with as little as 25% loss.

Infographic depicting SDMA detecting kidney disease when 25-40% of kidney function has been lost

So we’re now picking up the loss of kidney function earlier as marked in green on the graph below.

Infographic depicting earlier detection of kidney failure using SDMA

So how much earlier are we likely to detect kidney disease using the SDMA test when compared to the old creatinine test. In cats we anticipate picking up the disease 17 months and maybe even up to 48 months earlier so that’s a very significant improvement.

Infographic showing detection of kidney failure up to 48 months earlier in cats and up to19 months earlier in dogs

Not only will it pick up the disease earlier it’s also likely to make the diagnosis in a larger number of cases as illustrated in the image below from a study in America where 250,329 cats were tested and CKD in was diagnosed in 11% of cases without SDMA but when SDMA was used, CKD was picked up in 26% of cases.

Graph showing that SDMA can detect double the number of kidney failure cases compared with the old diagnostic tests
Prevalence with age of kidney failure and relative detection rates using SDMA and creatinine

Now, if we look at the age breakdown in image above it gets even more interesting. In this slide, the light blue boxes at the top represent the cases which would have been picked up using the old creatinine test and the red box underneath represents the cases that were picked up using the SDMA test.  So you can see that in cats aged 6-14 years, for every case this picked up using creatinine almost twice as many were detected using the SDMA. So only about 1/3 of cases using the old test in that age group of cats were being diagnosed!

IRIS Staging infographic

The above demonstrates the IRIS staging system IRIS stands for International Renal Interests Society. Basically, it’s a group of veterinary surgeons who got together and they’ve divided kidney disease into four stages; stage 1 being mild disease through to stage 4 being severe disease. You will notice that clinical signs i.e. the symptoms you as owners might pick up, only really become obvious once we get to stage three disease or beyond.

Clinical signs associated with kidney failure

So, what things MIGHT your cat do to try and attract your attention, what are the main clinical symptoms associated with CKD? The main signs are excessive drinking and excessive urination so you might notice that you’re having to fill water bowls and empty litter trays more often? Though a lot of cats go outside to drink and urinate so again this might not be too obvious to you. Other signs to monitor you cat for include decreased appetite in combination with weight loss.

IRIS Staging SDMA and its ability to detect kidney failure in stage 2 and possibly stage 1

So we’ve said that the clinical signs tend only to show relatively late in the disease process and that our current set of diagnostic tests that we have been using also tend to enable us to diagnose CKD at a late stage. This is where the SDMA comes hopefully enabling us to detect stage 2 or possibly even stage 1.

IRIS Staging SDMA staging graphic

Also, if we look at the level of SDMA  we may also be able to stage the disease as shown above.

How can we treat kidney failure?

 

Prescription kidney diet images

So, if we were able to make an earlier diagnosis what can we do about it. Well we might want to consider introducing a diet that supports kidney health or possibly if the disease is more advanced a therapeutic diet, there are a variety of these on the market in different formulation wet and dry.

A study published in the Journal of Small Animal Practice back in 2000 demonstrated that on average cats fed a renal therapeutic diet survive 2.4 times longer than cats fed on a maintenance diet 633 days versus 264 days. It would not surprise me with an earlier diagnosis that the difference in survival time would be even greater but obviously that has yet to be confirmed.

 

Monitoring kidney failure infographic

So, we made an early diagnosis and we’ve initiated a renal therapeutic diet. What other things might we want to monitor to ensure we maintain the health of your cat.  We will want to watch for changes in body weight, changes in appetite and overall demeanour. We will want to do some blood tests to check for the development of anaemia, monitor for changes to urea, creatinine, SDMA, phosphates and electrolytes. We might want to look at urine specific gravity, sediment and dipstick analysis and measure urine protein creatinine ratios. And we might want to keep an eye on your cats BP.

Urinalysis photo
Blood pressure measuring equipment photo

Now I’m indebted to Dr David Williams associate lecturer in veterinary ophthalmology at the University of Cambridge for very kindly allowing me to use the next two images to demonstrate the effects of high blood pressure secondary to chronic kidney disease in cats. In the first slide we see this very pretty tortoiseshell cat with the big black eyes due to massive pupillary dilation. Sadly this is not an uncommon presentation. These sorts of cats come to the surgery and I get them out of their box and as soon as I see these massively dilated pupils I fear the worst as it’s highly likely when I examine them that I’m going to find they’re blind. Sometimes these are cats that haven’t been presented to the surgery for a few years. They are often in good body condition and the owners are sadly blissfully unaware that their cat has any problems until they suddenly start bumping into things.

Blind hypertensive cat

Looking at the back of this cat’s eyes in the next image, we can see a red area which represents retinal bleeding. In an older cat the most likely cause is high blood pressure and one of the most common causes of high blood pressure in older cats is kidney disease.

Image of hypertensive cat's retina showing haemorrhage and detachment

In the most cats CKD is a progressive condition and it will become necessary to introduce medications such as phosphate binding drugs, potassium supplements and drugs which are designed to help the kidneys work better and reduce the tendency for proteins to appear in the urine.

Medications for the treatment and management of kidney failure
Sub cutaneous fluid therapy kit

I hope you’ve enjoyed this article and found it useful and I value your feedback on it.

If you are worried your cat or dog may have kidney failure and want to know more about having your pet’s kidney function checked using the new diagnostic test then please contact the surgery.