CKD is normally 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 Gastro-Intestinal
is the least invasive, because initially it does not require that you take
your cat to the vet.
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.
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
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
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 (renomegaly)
and he/she may also be able to feel scar tissue, although kidney palpation
alone is not sufficient for a diagnosis.
Most CKD cats,
though by no means all, have small, scarred kidneys.
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.
be performed on various parts of the body, usually the heart, abdomen or
In terms of
kidneys, an ultrasound allows the
vet to examine the kidneys to check their size and to look for certain
abnormalities in their shape or form. It normally looks at the following parts of the kidneys:
the outer part of the kidneys
the innermost part of the kidneys
the main cavity of the kidneys, which contains the renal pelvis, amongst
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.
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.
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."
Ultrasound: Who to Use
You need a
competent and experienced person to perform the ultrasound, ideally a
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 petís ultrasound is
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
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.
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.
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
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.
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
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
This may be
used in cases where cancer is suspected. Since it requires an anaesthetic,
it should only be done where absolutely necessary.
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." but Discuss this in more detail with your vet in case
there may be a valid reason in your cat's case.
cause enlargement of the kidneys with urine because of obstruction of the
ureter, which prevents urine from passing through. Cats with
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.
Acute uremia in cats (2008) Ross S Veterinary
Focus18(2) Dr Ross 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."