As discussed on the
Happens in CKD? page, it is normally not possible to detect CKD until the cat has
already lost 66-75% of his or her kidney function, although the new SDMA
test may change this.
This page discusses some areas of investigation into ways in which earlier
detection may be possible.
It is not currently possible to prevent CKD; but the earlier it is
diagnosed, the better your chances of helping your cat.
Benefits of Early Detection
It may appear
that there is no real benefit in early detection, because it is not
possible to cure CKD, and knowing at an early stage that your cat has it
may distress you. However, there are in fact some benefits to knowing
You can try
to find a cause and treat accordingly.
You can avoid
using potentially nephrotoxic treatments such as certain painkillers.
You can make
early changes that may be beneficial such as dietary changes.
You can take
appropriate precautions when treatments such as dental surgery are
You can watch
for urinary tract infections, which may further damage the kidneys.
monitor your cat for problems associated with CKD, such as high blood pressure
or anaemia, before these become severe and potentially life threatening.
You can avoid
your cat only being diagnosed following a sudden crash, with the
attendant risks and guilt.
Types of Test Available
standard for measuring kidney function in cats is via
glomerular filtration rate (GFR). Unfortunately this is not easily
measured in cats, so in practice the usual way to diagnose CKD has been
creatinine (and to a much lesser extent, BUN or urea) levels in the
blood, and via certain urine tests. However, creatinine does not tend to
rise in CKD cats until 60-70% of kidney function has already been lost,
which means that a cat can actually be in Stage 1 or 2 of CKD according to
the IRIS staging system (see
How Bad is
It?) but still have a creatinine that falls within supposedly normal
this, there have been many attempts to find a way of diagnosing CKD
earlier in cats. These tests are described below, but many of them are not
mainstream and are therefore either not widely available or are difficult to
use. The most useful one is probably going to be the new (2015) SDMA blood test.
SDMA is a methylated form of
amino acid. It is released when protein is processed, and is
eliminated largely (over 90%) by the kidneys. Because of this, it was
thought that increased levels of SDMA might correlate with the development
of CKD. One human study,
Symmetrical dimethylarginine: a new combined
parameter for renal function and extent of coronary artery disease
(2006) Bode-Böger SM, Scalera F, Kielstein JT, Martens-Lobenhoffer J,
Breithardt G, Fobker M & Reinecke H Journal of the American Society of
Nephrology17 pp1228-1134 concluded that "SDMA might be a
useful parameter for detecting patients in very early stages of chronic
kidney disease and for determining their risk for developing
The beauty of the SDMA test is that it can simply be
run as part of a standard blood chemistry blood test from IDEXX. In fact,
if you are in the USA and your vet uses IDEXX for blood chemistry panels,
the SDMA test will be provided at no additional charge during summer 2015.
If your vet uses in-house testing for most tests but has a relationship
with IDEXX, the test can be ordered separately from the IDEXX laboratory.
I have already seen a number of test results which include SDMA, but
that's not too surprising:
Reuters reports that more than 100,000
patients were tested in the two weeks following the test's launch in July
The test will become available in Canada in the summer
of 2015, and in Europe and other international markets in January
If your vet uses another laboratory such as Antech, you
can still request the test, but Antech will have to send it to IDEXX so
there will be a charge.
Interpreting the Results
IDEXX have provided the following guidelines for the
Early kidney disease
Over 20 ug/dl
More advanced kidney
IDEXX recommend that the test should not be run in
isolation but in conjunction with creatinine and urinalysis. Your vet
should also rule out
pre-renal causes and causes of
acute kidney injury.
IDEXX notes that for cats with SDMA and/or creatinine
at the upper end of the normal range, CKD cannot be ruled out, and
Only 1% of cats will have a reading over 50 ug/dl.
IDEXX explains what to do next if your
cat has a positive SDMA test. You can also read more about how to manage
your cat's current condition on the
is It? page.
SDMA FAQS answers frequently asked
questions about the SDMA test.
urine specific gravity may indicate loss of concentrating ability
before anything shows in bloodwork. However, a cat may have dilute
urine for other reasons, such as
so this is only a guide, not a definitive method of diagnosis. Also, once
a cat is receiving fluid therapy, USG can be rather unreliable.
The International Renal Interest Society
protein in the urine, which is known as proteinuria, as a risk factor for the development of CKD, and as a
determine the severity of the CKD.
Evaluation of predictors of the development of
azotaemia in cats (2009)
Jepson RE, Brodbelt D, Vallance C, Syme HM, Elliott J. Journal of Veterinary Internal Medicine23(4)
pp806-13 reports on a group of older cats who were monitored to see if
they developed CKD. The study concludes that "Proteinuria at presentation
was significantly associated with development of
azotemia although causal association cannot be inferred."
Protein in the urine may have causes other than CKD.
There is more information about proteinuria on the
If you know your cat
has proteinuria early on, you can take steps to control it, see
The following tests may be helpful in assessing the presence of
Idexx Laboratories offers a
test in a number of different countries which can calculate the
protein:creatinine ratio. It is part of their catalyst 1 test.
The E.R.D.-HealthScreen Urine Test
is another test which may assist with
detecting CKD in its early stages by detecting
low levels of protein (microalbuminuria) in the cat's urine. The
manufacturer claims that the test is able to detect cats at risk of CKD when there is as
little as 25% kidney damage, compared to the 60-70% loss of function that occurs
before anything shows up in creatinine levels.
The test is only available through your vet,
who has to run the test in-house. If your
vet does not have any in stock and you are in Europe, s/he can contact
Heska's European distributors
to obtain the test. Heska also has a list on its website of its
distributors in other parts of the world.
In the USA it should not cost more than US$20-30 if performed in addition
to other tests (Antech charges much less); it may cost slightly
more if run in isolation. Unfortunately, it appears to be much more
expensive in Europe, costing up to €200, though many vets will charge less.
The test is non-invasive, requiring only a urine sample, with
results available in-house in less than five minutes. If the test is positive,
further investigations should be performed, e.g. for high blood pressure.
The test may also be positive if certain inflammatory diseases such as IBD
or dental disease
are also present, or if the cat has certain other conditions such as
The International Renal Interest Society
states that the glomerular filtration rate (see
Happens in CKD) is "considered the single most useful and sensitive
test of renal function." IRIS believes that eventually GFR will be the
measure by which CKD can be categorised, although it will take some time
to determine appropriate reference ranges.
The main problem with measuring GFR is that it is quite
cumbersome, requiring the injection of contrast agents followed by
precisely timed blood tests. Therefore few vets are able or willing to do it.
Clearance Test (Plasma Iohexol Clearance
This test uses iohexol, an iodinated
radiographic contrast medium. Basically, the test measures how long it
takes to clear a measured amount of iohexol from the kidneys,
and this is then used to calculate the GFR. This test, sometimes referred
to as the Plasma Iohexol Clearance test (PIC) is highly
specialised and only available at a limited number of places in USA such
as the Animal Health Diagnostic Laboratory at Michigan State University; I
am not aware that the test is commercially available in Europe. This test
may be particularly helpful before opting for one of the more
permanent methods of treating
iohexol clearance test, the inulin clearance test measures how long it
takes the kidneys to clear a measured amount of a particular substance, in
this case inulin. This test only requires a single IV injection of inulin,
followed by the taking of a blood sample three hours later. The test is
already commercially available in Germany. This
test may be particularly helpful before opting for one of the more
permanent methods of treating
Fibroblast growth factor 23 (FGF23) is important for
the regulation of phosphorus levels in the body. Since phosphorus and
parathyroid hormone (PTH) imbalances are common in CKD, it is possible
that FGF-23 levels may in fact rise before other signs of CKD appear. In
humans, such increases have been identified before any changes in PTH and