Tanya's Comprehensive Guide to Feline Chronic Kidney Disease

This is usually one of the first questions people ask themselves after diagnosis.
This page attempts to help you understand a bit more about what the test results mean, and why they do not tell the whole story.
It also explains why it is not as bad as it sounds when your vet says your cat has lost a certain percentage of his/her kidney function.

Percentage of Function Lost

Let's get this out of the way first, because chances are things may not be as awful as you fear.

Most people panic if their vet says their cat has lost two thirds or more of his/her kidney function. I regularly hear from people who say things like "my vet told me my cat has lost 75% of kidney function so things look really hopeless".

Take a deep breath. I know it sounds like a massive loss of function, but it is actually completely normal for CKD not to be diagnosed until a cat has lost at least 66% of kidney function. In many cases the cat has lost even more kidney function. What Happens in CKD? explains why this is the case.

This may gradually change following the introduction in 2015 of the SDMA test, but even with this test, CKD cannot be detected until 40% of kidney function has been lost. So whichever way you look at it, your cat is unlikely to be diagnosed with CKD until a lot of kidney function is gone.

Some cats are diagnosed before they show any symptoms, perhaps because they have had annual blood tests run, and maybe their vet is using the RenalTech test. If your cat has not been acting sick despite having lost 66% or more of his/her kidney function, this demonstrates that cats can often manage very well on limited kidney function.

On the homepage I give my vet's analogy of a CKD cat being near the edge of a precipice. Another way to look at it is that your cat was edging through a door and has now crossed the threshold; but the kidneys have probably only lost a tiny bit more of the function they had a few months ago when your cat was a step further away from the doorway.

It is also quite possible that your cat was fine one day and sick the next. In these cases, something may have happened to push the cat through the doorway, such as an infection. Treating the cause may allow you to pull the cat fully or partly back outside the door.

In either case, the cat might linger in the doorway, not moving fully into the other room for some considerable time. Many cats can continue to manage quite well even after diagnosis -—for a small number of cats, things only become critical when they have lost as much as 90% of function, and there are some cats who cope astonishingly well with even less function. Renal dysfunction in small animals (2016) Brown SA Merck Veterinary Manual says "With appropriate therapy, animals can survive for long periods with only a small fraction of functional renal tissue, perhaps 5%-8% in dogs and cats."

So the goal is, not to worry about the function that has already been lost, but to try to help your cat manage with whatever function remains for as long as possible.

Chronic Kidney Disease versus Chronic Kidney Failure

You may also be frightened because your vet says your cat's kidneys have failed. Fortunately, this may also not be as bad as it sounds.

There are a number of different expressions used to describe chronic kidney disease. It used to be widely known as chronic renal failure (CRF), and for many years this website was known as Tanya's Comprehensive Guide to Feline Chronic Renal Failure.

I decided to change the name in 2011 and use the expression Chronic Kidney Disease (CKD) instead. This was for two reasons. Firstly, it is the term most commonly used in the academic literature. Secondly, I think it more accurately reflects the nature of the disease, and focuses on the important word, "chronic" rather than on that awful word, "failure", which tends to scare people, making them feel the end is nigh.

Chronic means that CKD is an ongoing disease. This is good news, because it means that in many cases it can be managed. For this reason, some vets prefer to use the word "insufficiency" for early stage cases instead.

Whatever expression your vet uses, try to focus on the chronic aspect of CKD.

Usual Tests For Assessing Kidney Function

The usual way for a vet to determine how advanced your cat's case is via blood tests. Many vets will also analyse your cat's urine (urinalysis).

In some cases, an ultrasound will also be appropriate.

Many vets now take the test results and categorise them according to IRIS staging of CKD (2023) International Renal Interest Society. This system divides CKD into four stages; so if your vet tells you, for example, that your cat is in Stage 2, s/he is probably referring to the IRIS staging system. There is more information about this below.

Remember, your cat's test results are only part of the story. There are other factors at play, including how your cat is acting, how proactive your vet is, whether there is an infection etc. For this reason, we have a mantra on Tanya's CKD Support Group: treat the cat, not the numbers.

Blood tests

Urine tests

Blood Tests

Your vet will test a number of measurements in your cat's blood, but the main measures of kidney function in bloodwork are:

Blood tests can tell vets quite a lot about how a cat's kidneys are functioning, but in some cases the results can be misleading. Blood drawn from a severely dehydrated cat, for example, will make the results look a lot worse than they actually are. In such a situation, the results may improve greatly once the dehydration is corrected (you are really just seeing the true situation). Similarly, bloodwork may look really poor in a cat with an infection but improve once the infection is under control.

Urine Tests

The urine tests will usually look at:

urine specific gravity (USG)
proteinuria (protein in the urine)
signs of infection

Urine specific gravity shows how concentrated your cat's urine is (CKD cats tend to have dilute urine). There is more information about this here.

Proteinuria is used by IRIS to help stage CKD (see below).

If your cat has an infection, this may make the kidney values in bloodwork look worse than they are. Unfortunately, in CKD cats infections do not always show in urine tests. There is more information about this here.

How Bad Are My Cat's Results?

Many vets now use the International Renal Interest Society's staging system:

IRIS Staging System

Staging of CKD (2023) International Renal Interest Society guidelines have four stages.

Staging should only occur after diagnosis. Before making a firm diagnosis of CKD, two blood test readings from a stable cat who is not dehydrated (dehydration can make the numbers look a lot higher than they really are) are required. Ideally the readings should be taken after fasting, though that is not always the best choice for a CKD cat. In practice, most vets will make the diagnosis based on bloodwork taken once during your initial visit, but remember, this is not optimum. And if your cat is in crisis, perhaps severely dehydrated and on a drip at the vet's, the blood test readings will not be accurate, so do not panic.

The IRIS stages contain indicate ranges, however, the range for the laboratory which your vet uses may be very different. See Test Ranges for more information about reference ranges.

The stages give some idea of how advanced your cat's case is, but also are there to help your vet come up with a tailored treatment plan.

IRIS looks at the following factors:

blood tests
- creatinine
- SDMA
proteinuria (protein in the urine)
hypertension (high blood pressure)
FGF23

IRIS Staging System: Blood Tests: Creatinine and SDMA

IRIS Staging: Creatinine

The IRIS staging system begins by looking at the cat's creatinine levels. Here are the four stages, together with my estimate of the likely percentage of function lost at each stage:

Stage of Disease	Blood Values: US Measurements (mg/dl)	Blood Values: International Measurements (µmol/L)	Approx. Level of Kidney Function Lost
Stage 1	Creatinine below 1.6	Creatinine below 140	0 - 65%*
Stage 2	Creatinine between 1.6 and 2.8	Creatinine between 140 and 249	66 - 75%
Stage 3	Creatinine between 2.9 and 5.0	Creatinine between 250 and 440	76 - 90%
Stage 4	Creatinine over 5.0	Creatinine over 440	Over 90%

Feline chronic kidney disease (2015) Grauer GF Today's Veterinary Practice 5(2) pp36-41 believes slightly different percentages of function are lost at the various levels of creatinine. He states "80% nephron loss may result in a serum creatinine concentration of 2 mg/dL. With progression, serum creatinine concentration should be approximately 4 mg/dL when 90% nephron loss has occurred." He adds "At the onset of International Renal Interest Society (IRIS) Stage 4 CKD (serum creatinine concentration > 5 mg/dL), it is likely cats have < 10% of their original nephron population."

So essentially Dr Grauer believes cats with a creatinine level between 2 and 4 mg/dl have lost 80-90% of kidney function. On the other hand, I attended a webinar with Dr D Chew in which he stated that a change in creatinine from 2 mg/dl to 4 mg/dl indicates only a 5% worsening.

Thus there is no consensus over how much kidney function has been lost at each stage. It is not that important though, what is important is how your cat manages with whatever function is remaining. Some cats manage really well with very little function: Renal dysfunction in small animals (2016) Brown SA Merck Veterinary Manual says "With appropriate therapy, animals can survive for long periods with only a small fraction of functional renal tissue, perhaps 5%-8% in dogs and cats."

Cats in Stage 1

Let's take a closer look at cats who are apparently in Stage 1, even though these values (creatinine below 1.6 mg/dl or 140 µmol/L) are normal in many laboratory ranges.

Obviously, not every cat with such values, which are within normal range for most laboratories, has CKD!

The problem is that when measuring creatinine alone, you cannot detect CKD until at least 66% of function has been lost, because before that there are usually no symptoms (see above). Therefore for cats in Stage 1 who do indeed have CKD, bloodwork values are usually within the normal range, and kidney problems would only be suspected if an anatomical or functional abnormality had been detected, or if the SDMA test result indicates a problem (see immediately below).

For some cats in this category there may be no evidence of CKD, but the cat is at increased risk of developing it in the future e.g. because of old age or exposure to medications harmful to the kidneys. So, for example, a 16 year old cat with creatinine below 1.6 mg/dl (below 140 µmol/l) would fall into this category (since around 30% of cats aged over 15 have CKD), whereas a two year old cat receiving no medications would not.

Feline chronic kidney disease (2015) Grauer GF Today's Veterinary Practice 5(2) pp36-41 says "Note that this staging system suggests that azotemia in cats begins with serum creatinine concentrations of 1.6 mg/dL or greater. However, serum creatinine concentrations must always be interpreted in light of the patient’s muscle mass, urine specific gravity (USG), and physical examination findings in order to rule out pre- and postrenal causes of azotemia." He also says "The staging system outlined in Table 2 is not used until the presence of CKD has been confirmed."

IRIS does allow for this in its guidelines, stating that if there is no evidence of CKD, the cat should be re-assessed in 2-3 months, and every three months thereafter if creatinine is increasing or every six months if creatinine is stable.

IRIS Staging: SDMA

Staging of CKD (2023) International Renal Interest Society also looks at SDMA, which is a newer test introduced by Idexx in 2015/2016. This test appears to be able to detect CKD earlier than the traditional bloodtests (see Early Detection), in some cases it may be able to detect CKD when perhaps only 40% of kidney function has been lost.

Stage of Disease	Creatinine	SDMA Measurement	Comments
Stage 1	Below 1.6 mg/dl Below 140 µmol/L	Below 18	If SDMA is increasing or is consisently above 14, CKD may be present.
Stage 2	1.6 - 2.8 mg/dl 140 - 250 µmol/L	18 - 25	This is considered by IRIS to be mildly increased.
Stage 3	2.9 - 5.0 mg/dl 251 - 440 µmol/L	26 - 38
Stage 4	Over 5 mg/dl Over 440 µmol/L	Over 38

For cats with persistently elevated SDMA readings, Staging of CKD (2023) International Renal Interest Society guidelines suggest changes in the stage of CKD the cat is deemed to be in as follows:

Creatinine Level	IRIS Staging Based on Creatinine Levels Only	SDMA Measurement	Revised IRIS Staging
Below 1.6 mg/dl Below 140 µmol/L	Stage 1	Persistently over 18	Stage 2
1.6 - 2.8 mg/dl 140 - 249 µmol/L	Stage 2	Persistently over 25	Stage 3
2.9 - 5.0 mg/dl 250 - 440 µmol/L	Stage 3	Persistently over 38	Stage 4

IRIS Staging System: Proteinuria

IRIS staging of CKD (2023) International Renal Interest Society then recommends sub-staging based on whether proteinuria is present.

Healthy cats only have tiny amounts of protein in their urine because their kidneys do not allow the protein to leak through. In CKD cats, this mechanism can be faulty and excess levels of protein in the urine, known as proteinuria but sometimes referred to as microalbuminuria, may occur.

The usual way to determine if a cat has proteinuria is via the urine protein:creatinine ratio (UPC). Three urine samples should be collected over a minimum period of two weeks before a conclusion is drawn.

Urine Protein: Creatinine Ratio	Proteinuria Status
Below 0.2	Non Proteinuric (NP)
Between 0.2 and 0.4	Borderline Proteinuric (BP)
Over 0.4	Proteinuric (P)

There is a correlation between the severity of proteinuria and the prognosis. Survival of cats with naturally occurring chronic renal failure is related to severity of proteinuria (2006) Syme HM, Markwell PJ, Pfeiffer D & Elliott J Journal of Veterinary Internal Medicine 20 pp528–535 found that cats with a urine protein:creatinine ratio below 0.5 survived almost three times as long as cats with a urine protein:creatinine ratio of over 0.5.

However, don't panic if your cat's level is over 0.4 because the UPC ratio is not always accurate; for example, blood in the urine, infection or inflammation may give a false positive result. Hypertension may worsen proteinuria, so getting blood pressure under control may lead to an improvement in the UPC ratio. Even if your cat's UPC ratio is indeed high, it may gradually reduce with treatment. Please see the Proteinuria page for more information.

IRIS Staging System: Hypertension

IRIS staging of CKD (2023) International Renal Interest Society then recommends substaging based on whether hypertension is present. It considers a cat's blood pressure in terms of how likely it is that damage to organs such as the eyes will be caused:

Average Systolic Blood Pressure Measurement (mmHg)	Risk of Damage to Organs	Blood Pressure Substage	Treatment Plan
Under 140	Minimal	Normotension	No treatment necessary
140 - 159	Low	Pre-hypertension	Treatment is not normally necessary. However, it may be appropriate to begin or increase blood pressure medications if ocular or neurological signs are present
160 - 179	Moderate	Hypertension	Begin or increase blood pressure medications
Over 180	High	Severe hypertension	Begin or increase blood pressure medications

For hypertension and severe hypertension, the readings would have to be persistently in these ranges for 1-2 weeks.

Hypertension is a very serious concern for CKD cats, so there is a separate Hypertension page.

FGF-23

In 2022 Idexx Laboratories introduced a new test called the FGF-23 test. This is not used to stage CKD but is used to guide when to start treatment for cats in early stage CKD whose phosphorus levels may appear normal but which in fact require treatment. Please see Early Detection and The Importance of Phosphorus Control for more information.

Treat the Cat, Not the Numbers

When vets tell people there is no hope for their cat, it is usually based on test results as outlined above, particularly blood tests which show high kidney values. However, I have heard of vets who tell people their cat should be put to sleep without doing any tests at all, based purely on the cat acting sick. I don't think this is appropriate. Your vet may be right, there may be no hope for your cat, but if you're thinking of making the irrevocable decision to put your cat to sleep, you need proper, accurate information on which to base your decision.

Even if you do have some blood test results, the numbers only tell part of the story. Prolonging the life of the renal failure patient (2000) Elliott J Waltham Focus 10(3) pp10-14 states that "in a retrospective study, the correlation between plasma creatinine and survival in cats who presented with signs of stable CKD was very poor, with only 5% of the variation in survival time being predicted by the initial plasma creatinine concentration".

Renal Disease (2006) Polzin DJ Delaware Valley Academy of Veterinary Medicine states "Severity of renal dysfunction as determined by serum creatinine concentration or measurement of GFR provides a less accurate means of assessing short-term prognosis than does the clinical condition of the patient. The relationship between magnitude of renal dysfunction and clinical signs of uremia is often unpredictable. Therefore, short-term prognosis should not be established on the basis of a single measurement of the severity of renal function. In addition, a single determination of renal function is unreliable as an index of the potential for improvement in renal function."

Finding the right balance: medical management of renal patients (2014) Vaden SL Eukanuba Veterinary Diets Clinical Symposium, Norway says "Attention should be given to the well-being of the patient rather than achieving a "magic" number for serum urea nitrogen or creatinine."

The laboratory diagnosis of feline kidney disease (2008) Heiene R Veterinary Focus 18(2) pp16-22 states "cats can sometimes, especially in cases of acute kidney injury secondary to obstructive FLUTD, develop creatinine values of 1600-1800 μmol/L (20.98-23.6 mg/dL) and yet recover."

So try not to worry too much about which stage your cat is in, especially since numbers can be artificially inflated at diagnosis. The stages are supposed to help the vet work out which treatments are likely to be needed, not encourage them to write off cats in the higher categories. Yes, your cat's chances may be worse if your cat is — and remains — a high numbers cat; but some cats do well despite high numbers, so try treating the cat, not the numbers and see what happens.

I don't know why some vets don't try to fight CKD. Perhaps they think it's not worth trying because CKD is incurable. Yes, CKD is incurable, but it can often be managed so your cat feels better. As one member of Tanya's CKD Support Group said, "vets are about the cure, we are about the care."

If your vet refuses to help, direct him or her to Treatment recommendations for CKD in cats (2023) International Renal Interest Society, which state "Although it is still important to administer treatments which slow progression of CKD, the importance of improving quality of life for these cats is greater at this stage.Therapies directly addressing clinical signs and aimed at improving quality of life include management of dehydration, acidosis, vomiting and nausea and anemia."

Therefore, if your vet has told you there is no hope for your cat, and has recommended euthanasia, I urge you to:

read this page, and also the Is There Any Hope? page to explore the various scenarios you may be facing;
check out the Index of Symptoms and Treatments page to see which symptoms your cat has; and
ask your vet about trying some of the Treatments that are appropriate for any of the symptoms you are seeing and any imbalances indicated by your cat's test results;

before making the irrevocable decision to put your cat to sleep.

What to Do At Each Stage

You may now know into which stage your cat falls, but that doesn't really tell you much about what you are facing on a practical level. And you still may not know how severe your cat's case is if your cat is in crisis. Let me repeat that:

Your vet cannot say how severe your cat's case is if your cat is in crisis.

So if your cat appears to be in Stage 4, don't despair. You may not be seeing the true situation. IRIS staging of CKD (2023) International Renal Interest Society says that "Staging is initially based on fasting blood creatinine assessed on at least two occasions in the stable patient", but your vet may have forgotten this. Bloodwork can look high for the following reasons:

the cat is severely dehydrated
the cat has an untreated urinary tract infection or a kidney infection
the cat has untreated hypertension (high blood pressure)
the cat has kidney stones

If any of these problems are present, they need to be treated and your cat stabilised before you can make an accurate assessment of your cat's situation.

Staging is not only about how severe the CKD is. It is intended to help with treatment plans. You should monitor for:

so you can nip these problems in the bud if they are present.

The most important thing for cats in all stages is to get food into them! See Persuading Your Cat to Eat for tips and hints.

You should also consider that nobody knows how fast your cat will progress through the stages. Even if your cat is in Stage 4, you do not know if this will stay the same or worsen quickly. Feline chronic kidney disease (2015) Grauer GF Today's Veterinary Practice 5(2) pp36-41 states that although CKD is irreversible, "some cats with CKD have stable serum creatinine concentrations for months to years."

In virtually all cases it is worth trying treatments for at least two weeks. Treatment recommendations for CKD in cats (2023) International Renal Interest Society have some suggestions on what to watch for and be prepared to treat at each stage, including what to do if proteinuria or hypertension are present.

Whatever stage your cat is at, most people find the treatments only take about 20 minutes out of their day, including the time needed to give subcutaneous fluids if necessary.

Here are some tips on what you may be facing:

Cat in IRIS Stage 1, Stage 2 or the Lower End of Stage 3

If your cat seems to fall into IRIS Stage 1, 2 or the lower end of Stage 3, it is early stage and with proper care and a little luck on your side, your cat could live for years.

Most cats in these stages (creatinine below 3.5-4.0 mg/dl US or 300-350 µmol/L international) will not need subcutaneous fluids and can easily be managed with just a few treatments tailored to the individual cat's needs, e.g. treatment for nausea, constipation and/or control of elevated phosphorus levels.

If your cat has proteinuria or hypertension, these should be properly controlled.

In all cases, it is essential that your cat eats!

Cat in Stage 4 or the Upper End of Stage 3

If your cat seems to fall into Stage 4 or the top end of Stage 3, don't despair. You may not be seeing the true situation. Bloodwork can appear high for the following reasons:

severe dehydration
an untreated urinary tract infection or a kidney infection
untreated hypertension (high blood pressure)
kidney stones

In such cases, the numbers you are seeing won't be an accurate representation of true kidney function. Feline chronic kidney disease (2015) Grauer GF Today's Veterinary Practice 5(2) pp36-41 says "This staging system cannot be applied to patients with pre- or postrenal azotemia or those with acute or acute-on-chronic kidney disease." You need to treat your cat, particularly any dehydration, before you can know the true status of the kidneys.

If your cat has moved to Stage 3 or 4 from an earlier stage, especially if this has happened abruptly, the same principle applies: make sure any possible causes of the worsening bloodwork have been treated.

Even if your cat proves to be at the top of Stage 3 or in Stage 4 following stabilisation, don't give up hope: some cats do seem to manage very well on very little kidney function, and it is possible that your cat could be one such cat. You will probably need to be more proactive and your cat will usually need more treatments than cats with lower bloodwork values, but it is certainly worth trying to help.

These cats will usually need the same treatments as cats in lower stages for whatever problems may be present, e.g. for nausea, high phosphorus levels, constipation etc. In addition, they will usually need regular fluid therapy in the form of subcutaneous fluids in order to avoid dehydration.

Cats in IRIS Stage 4 will often have anaemia, and will need treatment for that - untreated severe anaemia can be very dangerous and can kill a CKD cat before the CKD does. Fortunately, many effective treatments for anaemia are available, meaning no CKD cat need die of anaemia. See the Anaemia page for more information.

Cats in IRIS Stage 4 may have metabolic acidosis, so ensure your vet checks for that and treats it if it is present.

Treatment recommendations for CKD in cats (2023) International Renal Interest Society, which state "Although it is still important to administer treatments which slow progression of CKD, the importance of improving quality of life for these cats is greater at this stage.Therapies directly addressing clinical signs and aimed at improving quality of life include management of dehydration, acidosis, vomiting and nausea and anemia."

Please see the Is There Any Hope? page for more information.

If your cat's creatinine levels improve, this usually indicates that your cat is doing better. However, occasionally creatinine falls because of muscle loss (because creatinine is a by-product of muscle). Overview of the urinary system (2016) Sanderson SL Merck Veterinary Manual states "Serum creatinine levels can be falsely decreased in patients with severe muscle wasting." So if your cat's creatinine level falls but your cat has lost a lot of weight and muscle, this might be the cause rather than improved kidney function.

End Stage Renal Disease (ESRD)

This expression literally means that the cat's kidneys are at the point of failure and there is no longer anything that can be done. Some vets use it in this sense, referring to a cat who is rapidly becoming unable to deal with the CKD, ceasing to respond to treatments and likely to die very soon. However, other vets use it to mean any cat with numbers in Stage 2 or above (see above), when in fact many cats in these stages can live for a long time.

Try to clarify what your vet means by ESRD, and if s/he merely means that your cat has high numbers, consider treating the cat; the numbers may come down with treatment, and even if they don't, your cat might be able to handle high numbers as Thomas did. Even if your vet thinks death is imminent, it may be worth treating your cat regardless to see how he or she responds; cats are real fighters and can often pull through.

Obviously though, you don't want your cat to be in pain when it is a hopeless situation. It is not always easy to tell when a CKD cat has come to the end of the road, so The Final Hours contains details of the symptoms you are likely to see towards the end, and discusses making the painful decision to let go.

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This page last updated: 04 March 2023

Links on this page last checked: 26 June 2020

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TREATING YOUR CAT WITHOUT VETERINARY ADVICE CAN BE EXTREMELY DANGEROUS.

I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who has lived through CKD with three cats. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.

If your cat appears to be in pain or distress, do not waste time on the internet, contact your vet immediately.

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