diagnosing renal disease in cats



Diagnosing Chronic Renal Disease

There has been a recent exciting development in diagnosing Chronic Renal disease:  the SDMA test.

The test is exciting as it seems it will allow the diagnosis of CRD much much earlier than is now possible  – and the earlier people are aware their cat is showing signs of CRD, the earlier they can take steps to try and help slow the progression of the disease.

The test is being rolled out, and is not yet available everywhere (see more information below).

The current tests are available at any vet clinic, and while much more kidney function has been lost before they detect the disease, they will certainly remain the main diagnostic method to determine CRD for the near future at least.   It is likely that they will remain the norm in many countries or areas for quite some time simply as most vets with lab equipment can do these tests themselves vs. the SDMA test, which is only done by IDEXX labs.

Diagnosing Chronic Renal Disease

The most widely available tests for CRD

Currently,  diagnosis of CRD is made using the following three exam results (available everywhere). All three together are needed to confirm the disease:

1) High BUN or Urea
2) High Creatinine
3) Low Urine Specific Gravity (or USG)

In addition, high phosphorous levels help to confirm the diagnosis.

It is important that all three tests show the above results – individual results for one or the other factors can influenced by a number of factors. One or two abnormal results do not necessarily mean CRD is present. All three are needed to confirm the result.

BUN/Urea measures the level of urea, which is a by-product of protein metabolism excreted by the kidneys.
BUN/Urea levels can be high for several reasons that have nothing to do with CRD:

• A high protein diet – ‘normal’ values are not set to cats that are on a low carb/high protein diet – as is the case for our FD cats!
• Dehydration is a common cause of high BUN/Urea levels
• Blockage of the urethra
• Gastro-intestinal bleeding
• Some medications – Anti-inflammatories, certain antibiotics (abx)

Creatinine is a waste product that is the result of muscle metabolism. In general, it is considered a more accurate measurement of kidney problems as it is not affected by things like dehydration as is the case for BUN/Urea.

However, there can also be other reasons for a high Creatinine reading, including the following:

• Ketones/ Diabetic Ketoasidosis (DKA)
• Kidney infections
• Kidney stones
• Inflammation
• Hypertension
• Pancreatitis
• A cat that is heavily muscular – more muscle means more muscle metabolism

Urine Specific Gravity (USG)
USG measures if the urine is concentrated or diluted. More diluted urine can indicate CRD. As for both BUN/Urea and Creatinine, there can be other reasons for a more diluted urine.

Low USG results may be due to:

• Simply eating wet food vs. dry – cats do not drink enough to make up for the lack of moisture in dry food. Cats on wet food will have more liquid, so more liquid to expel, than those on dry foods
• Unregulated FD cats that are drinking a lot because of the high BGs will have more diluted urine

In general, a cat with a USG below 1040 is considered to have a problem of some kind. In the case of CRD, most cats who are suffering from the disease will have a USG under around 1012.

The SDMA test:  a recent break-through in CRD diagnosis

There has been a recent break-through in discovering CRD at early stages: The SDMA (symmetric dimethylarginine) test that has been developed by IDEXX. It can discover signs of CRD months or even years before the tests outlined above.

Today, usually at least 70% of kidney function is lost by the time kidney disease is apparent via current lab tests (BUN/Urea, Creatinine and USG). IDEXX claims that their test diagnoses the disease when only 40% of kidney function is lost.

IDEXX is including their test in standard test runs at no extra charge.

The exam is being rolled out in the US this year (2015) and should be available throughout the country by fall 2015. Worldwide rollout is planned for 2016.

More information can be found in the links at the end of this article.

This new exam is exciting news; it is the first exam that does allow finding CRD at an early stage – allowing you to start treating CRD much more quickly and to help your cat live much longer with the disease.

CRD Stages

CRD is usually discussed in terms of what stage it is in: you may be told by your vet that your cat has Stage 2 or Stage 3 CRD, for example.
The stages referred to are based on Creatinine levels, and were developed by IRIS, the International Renal Interest Society. These stages are accepted worldwide as a measure of the severity of the disease.
The creatinine stages are a starting point: IRIS recommends then taking into consideration protein levels and hypertension to create sub-stages.

With the new SDMA test, preliminary new stages are now being recommended.

The table below shows the IRIS Stages before the SDMA, Clinical signs and Actions to Take.

It is important to note that:

1) Clinical signs of CRD are not (or barely) present in Stages 1&2. Clinical signs of CRD do not show until Stage 3.
2) The “Actions” are guidelines, depending on the individual cat, treatment may be needed for certain issues sooner or later than noted
3) Stage 1 refers to cats that DO have CRD. Creatinine blood values are normal. It is only other symptoms such as dehydration, hypertension and or proteinuria that may lead to a possible CRD diagnosis at this point.

Feline Renal Disease Stages


The new staging is attacking CRD earlier and more proactively than the old and is recognising that CRD is present before current testing or clinical signs have been able to diagnose it – all of which is very good news for getting cats the help they need more quickly.

CRD and Food

One of the first things people are told with a CRD diagnosis is that they must immediately switch their cat to a special vet renal food.

Please do not!

Most renal foods are based on reducing protein: the high protein carnivore diet our cats need does lead to higher levels of protenurea (protein urine levels) and to high phosphorous – a result of the high meat content.

Cats NEED a high protein diet, though – they are obligate carnivores.

Renal foods restrict protein by increasing something else: carbohydrates, simple filler, etc. They do not necessarily provide anything close to the balanced – protein based – diet that your cat needs.

There are nonetheless a number of things that you CAN do to provide the diet that your CRD cat needs:

1) Do try and find a low-carb wet food with lower phosphorous levels. Dr. Pierson’s list, if compiled in 2012, is a good starting point to try and find the right balance between low carbohydrates and lower phosphorous levels if you live in the US: Dr. Pierson’s Food List
2) Lightly cooked egg-whites are an excellent source of low phosphorous protein for you cat: try replacing some of your cat’s food with them. Note: they DO need to be cooked, raw whites interfere with B vitamin absorption. Egg yolks are very high in phosphorous, so do give only the cooked whites!
3) Choose your proteins: while there is not a big difference, all helps. Chicken is one of the lower phosphorous proteins while pork and rabbit amongst the highest. Incidentally, by far the highest is a mouse – the cat’s normal food!
4) Adding Omega-3 can really help – this is often added in “special” renal food and it does make a difference. You can use fish or krill oil for that – do check to make sure that it is purified and that heavy metals/toxins are guaranteed as having been removed.
5) Many “special” renal foods also add extra B12 – you can and should be supplementing with this (see treatments below)

The absolute worst thing you can do is to put your cat on a special dry food renal diet: cats need the moisture they get from wet food when they are healthy; when suffering from CRD the need is even more critical.

For information on Treatments & Additional Links please continue on page 3.


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