CKD is normaly diagnosed via blood tests and
urinalysis (urine tests).
Sometimes other tests may be appropriate, for example,
if a kidney infection is suspected, or if a young cat has CKD.
The tests below are listed in order of invasiveness.
Occult Blood Test for Gastrointestinal
Bleeding
This test
is the least invasive, because initially it does not require that you take
your cat to the vet.
If you
suspect that your cat has gastrointestinal bleeding (which could be the
case if your cat's
BUN:creatinine ratio is high,
PCV or HCT is falling and
albumin and/or the
MCV are low), you should take a
stool sample to your vet for testing and ask for an occult blood test.
I did this
test when Ollie was anaemic. My vet had never been asked to do this test
before, but Ollie's test was positive.
You
can buy the
EZ Detect test from pharmacies, which
tests for blood in the stool or urine (this is a human test but can also
be used for cats). You can drop some of your cat's stool in the toilet and
then follow the instructions on the packet.
Do not give
iron supplements for a couple of days before obtaining a sample for
testing. Ideally you should also feed no red meat products
beforehand, because red meat may give a false positive. I was reluctant to
restrict Ollie's diet because he was already anaemic and not eating too
well, but Ollie seemed to do well enough on chicken-based foods. Do check
what you are feeding though, many commercial foods contain more than one
meat source.
Pilot study of the effect of gastrointestinal diets on fecal occult blood
testing in cats (2020) Spies KE & Slovak JE Journal of
Feline Medicine and Surgery22(7) pp656-663 found that faecal
occult blood testing could be effective in cats, and found that feeding "a
single dry hydrolyzed, dry gastroenteric or canned hydrolyzed diet in this
study had a low chance of false-positive FOB test results, while those fed
the canned gastrointestinal diet had a significantly greater likelihood of
producing false-positive results."
Sensitivity of fecal occult blood testing in the cat
(2017)
Rudinsky AJ, Guillaumin J & Gilor C Journal of Feline Medicine and
Surgery19(6) pp603-608 recommends that the test should be run
"in strict clinical conditions, including a controlled diet, adequate
washout period prior to testing, and no medication, which could interfere
with results."
Both tested kits are
clinically useful for occult blood in cat feces; however, the diet fed
prior to testing must be taken into consideration, and dietary
restrictions are advisable before testing."
Palpation of Kidneys
If you visit
your vet because you are worried your cat might have CKD, the first thing
your vet will do is usually a physical examination of the kidneys by
palpating (feeling and moving) them through the skin. This will tell your
vet whether the kidneys feel small or large
and he/she may also be able to feel scar tissue.
Most CKD cats
have small, scarred kidneys, because their kidney damage is caused by
chronic
interstitial nephritis. However, some CKD cats have enlarged kidneys (renomegaly).
Kidney palpation
alone is not sufficient for a diagnosis.
Oral Checks
Many cats with
CKD have dental problems, which in some cases may even have contributed to
the development of CKD. It is therefore important for your vet to keep a
close eye on your cat's mouth and to treat any dental disease, and also to
look for mouth ulcers. Most vets will examine your cat's mouth routinely
at visits, but many dental problems are invisible to the naked eye.
Ultrasounds can
be performed on various parts of the body, usually the heart, abdomen or
kidneys.
Ultrasounding
the
kidneys allows the vet to check their size and to look for certain
abnormalities in their shape or form. An ultrasound normally looks at the following parts of the kidneys:
renal cortex:
the outer part of the kidneys
renal medulla:
the innermost part of the kidneys
renal sinus:
the main cavity of the kidneys, which contains the renal pelvis, amongst
other things
The renal pelvis
is the top of the ureters (the tubes that lead to the bladder). It is not always looked at
on ultrasound, though it can be helpful for some diagnoses.
Ultrasounds are
not invasive and can usually be done without anaesthesia or even sedation,
so there is no need to fast the cat beforehand. The cat may need to
be shaved at the examination site (although my extremely fluffy Chinchilla
had a cardiac ultrasound without being shaved). Cold gel has to be
applied to the body to allow the equipment to work properly, which may be
a little uncomfortable when first applied (ask if you can warm it a little
in your hands first), but all my cats who have had
ultrasounds coped just fine.
enlarged kidneys
(renomegaly). Most
CKD cats have small, shrivelled kidneys.
It was
thought that ultrasounds are unlikely to be worthwhile for
the diagnosis of CKD.
Ultrasound of cats with chronic renal disease
(2007) Zwingenberger A Veterinary Radiology says ""Although ultrasound is able to detect changes in chronic renal disease,
it is not highly sensitive. Cats can have significant renal dysfunction
without ultrasonographic signs of renal disease. Conversely, many cats
cope with their chronic renal disease though they have severe
ultrasonographic changes. The history and bloodwork are important in
assessing the significance of the findings."
However, recent research indicates that all CKD cats could benefit from an
ultrasound at initial diagnosis.
Pilot study to evaluate the potential use of the
renal resistive index as a preliminary diagnostic tool for chronic kidney
disease in cats (2018) Matos I,
Azevedo P & Carreira LM Journal of Feline Medicine and Surgery20(10) pp940-947 looked at using ultrasound to assess the use of the renal
resistive index to help diagnose in CKD cats. The study found "No
differences were found for the RRI between the left and right kidneys,
suggesting that evaluation of only one kidney is sufficient to provide an
estimate of the RRI value for both organs. RRI measurement, which can be
achieved with CDUS [colour doppler ultrasound], is an easy-to-use
diagnostic tool that, with a cut-off value of 0.639 for both kidneys, is
useful in establishing a preliminary diagnosis of CKD."
Renal pelvic and ureteral ultrasonographic
characteristics of cats with chronic kidney disease in comparison with
normal cats, and cats with pyelonephritis or ureteral obstruction
(2017) Quimby JM, Dowers K, Herndon AK, Randall EK Journal of
Feline Medicine and Surgery19(8) pp784-790 found that the renal
pelvis
(the upper end of the ureter)
could be dilated (this is known as pyelectasia) in cats with CKD (up to
two thirds of the cats in the study had pelvic dilation of 1.2mm up to
11.5mm), as well as in cats with
pyelonephritis and kidney stones and states "these data suggest CKD cats
should have a baseline ultrasonography performed so that abnormalities
documented during a renal crisis can be better interpreted."
Therefore, if
you can afford it, I would consider an ultrasound when your cat is first
diagnosed. It is not usually necessary to sedate a cat for an ultrasound,
nor is fasting required.
Ultrasound: Who to Use
You need a
competent and experienced person to perform the ultrasound, ideally a
radiologist.
What you should know about your pet's ultrasound
exam (2009) Murray L Vet Confidential states "If your pet
ever needs an ultrasound exam, it's crucial to ensure that it's done
properly. An inadequate ultrasound can be worse than none at all, since it
often leads to misdiagnosis, which can be very dangerous for your pet. The
use of ultrasound in veterinary medicine has become very common but there
are no regulations in place to ensure that your pet’s ultrasound is
performed competently."
Sometimes you
may be offered the option to have the ultrasound performed by your vet who
will then send the images to a radiologist for feedback. Dr Murray goes
on to say
"Unfortunately many mistakes can
occur with this method. If an abnormality is not recognized by the
untrained person performing the exam, or the images are of poor quality,
the radiologist cannot make an accurate assessment of the animal. This
technique should be a last resort, for geographic areas where there is
no radiologist or internist available."
Renal ultrasound Blok BK & Hoffmann B
Ultrasound Guide for Emergency Physicians: An Introduction is about
humans and is quite technical, but it has some kidney images you may find
helpful.
Ultrasound: Findings
The kidneys of a typical healthy cat will be between 3 and 4.3 cm (around
1.25 to 1.75 inches) in length, though in some cats they may be a little
longer. The size of the cat is a factor, with females tending to have
smaller kidneys than males.
Healthy kidneys are oval or shaped like a bean, and smooth.
CKD cats tend to have small, shrivelled kidneys with an irregular shape.
Ultrasound of cats with chronic renal disease
(2007) Zwingenberger A Veterinary Radiology explains more about
what normal kidneys look like on ultrasound, and what differences you may
see in CKD and end stage CKD kidneys.
In cases of kidney infection (pyelonephritis), the renal pelvis may be dilated (this is known as
pyelectasis), which should be visible on ultrasound (though this may not
occur in the case of acute infections). This dilation may also occur when
kidney stones or other obstructions are present,
though will usually be more severe.
Feline chronic renal disease — acute presentation
(2007) Zwingenberger A Veterinary Radiology explains more
about how acute kidney injury looks on ultrasound, including information
on cases of obstruction or pyelonephritis.
X-rays can be
used to look at the kidneys and to check for kidney stones, but in most cases
palpation and, if necessary, the use of ultrasound make the use of x-rays
unnecessary.
For fractious
cats, x-rays may
require the cat to be sedated. Some members of
Tanya's CKD Support Group have been allowed to
don lead aprons and hold their cats still for the x-ray instead, but not
every vet permits this.
Renal imaging in cats (2008) Seyrek-Intas
D & Kramer M Veterinary Focus18(2) pp23-30 discusses
x-rays.
Intravenous Pyelogram (IVP)
An IVP is a special type of X-ray which uses a contrast agent to clearly
show the urinary tract.
IVPs may be used when tumours or blockages are suspected. However, the
dyes used as a contrast agent may be toxic to the kidneys, particularly if
there is a blockage. The dyes are also excreted by the kidneys, which is a
risk for cats with advanced CKD. These risks must be borne in mind when
deciding whether to have this procedure.
This is a helpful way of evaluating kidney function and does not
require anaesthesia in most cases. However, it is only available at a
small number of centres, so is normally only used to
assess kidney function prior to removing a kidney because of a tumour or
prior to a nephrectomy (cutting into the kidney, e.g. to remove kidney
stones). It is unlikely to be of any benefit for the typical CKD cat with
small, scared kidneys.
Renal imaging in cats (2008) Seyrek-Intas
D & Kramer M Veterinary Focus18(2) pp23-30 discusses planar
renal scintigraphy.
Biopsy
A kidney biopsy is occasionally recommended, but snce it requires an
anaesthetic, it should only be performed when absolutely necessary. Renal
biopsy: a retrospective study of methods and complications in 283 dogs and
65 cats (2005) Vaden SL, Levine
JF, Lees GE, Groman RP, Grauer GF & Forrester SD Journal of Veterinary
Internal Medicine19(6) pp794-801 states that complications
(usually severe haemorrhaging) were reported in 18.5% of the cats in the
study, and 3.1% died.
A biopsy may be performed in cases where cancer is suspected.
Persistent and severe proteinuria (UP/C>2.0) in a non-azotemic patient
Worsening proteinuria in a CKD patient
Acute kidney injury, where renal biopsy may provide a prognostic
indicator."
For general CKD
cases, it is unlikely that a biopsy will be of sufficient value to justify
the risks associated with it.
Choosing the right biopsy for the job
(2006) Wilcock B HistoVet states "With careful assessment of serum
biochemistry and urinalysis, biopsy is rarely indicated and (except for
glomerular disease) almost impossible to interpret." Discuss this in more detail with your vet in case
there may be a valid reason in your cat's case.
If your cat
does require a biopsy, read the guidelines on
anaesthesia for CKD
cats.
Renal disease/urology (2003) Ross SR has a section entitled A special
note on renal biopsies! (scroll down a little to find it).
Renomegaly (Enlarged Kidneys)
Most CKD cats have small, scarred kidneys,
but some kidney-related conditions may cause the opposite problem of
enlarged kidneys. These conditions are discussed in more detail elsewhere
on the site:
Hydronephrosis may
cause enlargement of the kidneys with urine because of obstruction of the
ureter, which prevents urine from passing through. This is commonly caused
by kidney stones. Cats with
acute kidney
injury may have enlarged kidneys, often (but not always) because of
such an obstruction.
Occasionally a cat will have one small kidney and one large kidney, a
condition known with startling originality as "big kidney little kidney
syndrome". This is commonly caused by
stones or obstructions. One
kidney becomes damaged by stones and shrinks, while the other increases in
size in order to compensate and take on some of the work of the damaged
kidney.
Acute uremia in cats (2008) Ross S Veterinary
Focus18(2) says "Sustained obstruction leads to fibrosis and atrophy
of the corresponding kidney and compensatory
hypertrophy of the contralateral kidney. The
disease remains clinically silent until obstruction
of the contralateral ureter occurs. This process
explains the classic "big kidney-little kidney"
scenario typical of many cats diagnosed with acute ureteral obstruction."
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.
This site was
created using Microsoft software, and therefore it is best viewed in
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browsers, but I'm not an IT expert so I'm afraid I don't know how to
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is on making the information available. When I get time, I'll try to
improve how it displays in other browsers.
This site is a labour of love. Please do not steal from me by taking credit for my work.
If you wish to
link to this site, please feel free to do so. Please make it clear that
this is a link and not your own work. I would appreciate being informed of
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