As discussed on the
Happens in CKD? page, it is not normally possible to detect CKD until the cat has
already lost 66-75% of his or her kidney function, although the SDMA test
may offer earlier indications of a problem.
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
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.
CKD early diagnosis
(2019) Syme H International Renal Interest Society
explains more about early detection and suggests obtaining baseline
bloodwork when your cat is healthy, so you can monitor trends for your
Types of Test Available
filtration rate (see
below) is the gold standard for
assessing kidney function in cats. Unfortunately GFR is not easy to
measure in cats, so although I do discuss it below, you are unlikely to be
offered this test unless you attend a vet school.
Historically, the usual way to diagnose CKD
in cats 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
limits. In addition, since creatinine is a by-product of muscle and is
higher when a lot of muscle is present, a large
muscular cat may be suspected of having CKD when he does not, whereas a
CKD cat who has lost a lot of weight and muscle might not be diagnosed
Because of this, there have been many attempts to find a way of diagnosing
CKD earlier in cats. The SDMA test was introduced in 2015 and
is now routinely offered.
Other Diagnostic Tests to read about an initial study into the
possible use of ultrasound to diagnose CKD in cats.
Biomarkers of kidney disease: potential utilities
(2018) Segev G International Renal Interest Society
discusses the benefits of early detection and mentions some possible
tests, though none of these is widely available as yet apart from the SDMA
Most vets will check your cat's
(or urea) levels. You may also be offered the SDMA test.
(Symmetric Dimethylarginine) Test
What is SDMA?
SDMA is a methylated form of arginine, an
amino acid. It is released when protein is processed, and is
eliminated largely (over 90%) by the kidneys. Because of this, increased levels of SDMA may correlate with the development
IDEXX states that the SDMA test can
therefore potentially detect CKD when up to 40% of function has been lost, whereas
traditionally you could only detect CKD when 60-70% of function had been
More than 100,000
patients were tested in the two weeks following the test's launch in July
2015. The test became available in Canada in the summer
of 2015, and in Europe and other international markets in January
SDMA: How to Run
The SDMA test can simply be run as part of a standard
blood chemistry blood test from IDEXX. If you are in the USA and your vet
uses IDEXX for blood chemistry panels, the SDMA test should be provided
routinely. 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
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
Only 1% of cats will have a reading over 50 ug/dl.
IDEXX recommend that the test should not be run in
isolation but in conjunction with creatinine and urinalysis.
should also rule out
(such as dehydration) and causes of
acute kidney injury
(AKI) because SDMA may be elevated in cases of AKI or if any other
condition is present that
reduces blood flow through the kidneys.
Symmetric dimethylarginine in cats with hypertrophic
cardiomyopathy and diabetes (20180
Langhorn R, Kieler IN, Koch J, Christiansen LB & Jessen LR Journal of
Veterinary Internal Medicine32(1) pp57-63 looked at SDMA levels in cats
with HCM or diabetes. It concludes "Serum SDMA concentrations in cats with
HCM were not significantly different from those of healthy control cats.
Cats with DM, however, had significantly lower SDMA concentrations than
controls, a finding that needs further investigation and should be kept in
mind when evaluating renal function of cats with this endocrinopathy." I
take this to mean that a cat with both CKD and diabetes might have lower
SDMA levels than if the cat had CKD only.
Creatinine levels are naturally higher in Birman cats,
which may lead some Birmans to receive an incorrect diagnosis of CKD.
Serum symmetric dimethylargininr and
creatinine in Birman cats compared with cats of other breeds
(2018) Paltrinieri S, Giraldi M, Prolo A, Scarpa
P, Piseddu E, Beccati M, Graziani B & Bo S Journal of Feline Medicine
and Surgery 20(10) pp905-912 found that levels of SDMA are also
higher in Birman cats, though not as much as creatinine. The study states
that Birman cats should be assessed based on SDMA as well as creatinine,
and using a specialised reference range for Birmans.
IRIS staging of CKD
(2019) International Renal Interest Society refers to SDMA results in
its staging guidelines. For cats with persistently elevated SDMA readings,
it suggests changes in the stage of CKD the cat is deemed to be in as
Staging Based on Other Criteria
Revised IRIS Staging
Over 18 ug/dl
Stage 2 but with a
low body condition score
Over 25 ug/dl
Treat as if in Stage
Stage 3 but with a low body condition score
Over 38 ug/dl
Treat as if in Stage
SDMA: What To Do Next
IDEXX SDMA algorithm
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.
Urine specific gravity (2015) Watson ADH,
Lefebvre HP & Elliott J International Renal Interest Society has information on the significance of USG in cats.
Proteinuria (2016) Grauer GF International
Renal Interest Society explains how
protein in the urine, which is known as proteinuria, is a risk factor for the development of CKD, and also a
determining 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
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.
A similar test is also available from Antech.
an artificial intelligence (AI) predictive tool developed by Antech, which
claims it can detect CKD up to two years earlier than other methods, and
with 95% accuracy in some cases. The system assessed the records of more
than 100,000 cats who visited a chain of veterinary clinics three or more
times between 1995 and 2017.
Predicting early risk of chronic kidney disease in
cats using routine clinical laboratory tests and machine learning
(2019) Bradley R, Tagkopoulos I, Kim M, Kokkinos Y, Panagiotakos T,
Kennedy J, De Meyer G, Watson P & Elliott J Journal of Veterinary
Internal Medicine33(6) pp2644-2656 explains more about how the
tool was developed.
The test results needed to use the tool are ones you would usually be
Glomerular filtratrion rate in dogs and cats
(2013) Heiene R & Lefebvre HP 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." It is also the best way to detect CKD early
because GFR reduces before a rise in creatinine is apparent. It goes on to
say "Assessment of GFR is therefore pivotal for evaluating severity and
progression of renal diseases, especially chronic kidney diseases (CKD)."
Unfortunately measuring GFR 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.
Early diagnosis of chronic kidney disease in dogs
and cats: use of serum creatinine and symmetric dimethylarginine
(2016) Grauer GF Today's Veterinary PracticeMar/Apr 2016
states "due to expense, time, and labor, GFR is rarely measured in the
practice setting." GFR measurement is available at most vet schools and I
understand the Royal Veterinary College can do it for around £180 (2016
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. Some people use this test
before opting for one of the more permanent methods of treating
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.
Practical matters: practical ways to
measure GFR in your patients
(2011) Langston CE Veterinary Medicine explains more about
how the test is performed and says "Although
iodine allergic reaction or development of mild reversible acute kidney
failure has been reported in people undergoing this type of test, the risk
in animals appears to be low."
Fibroblast growth factor 23 (FGF-23) is important for
the regulation of phosphorus levels in the body. Since
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
This study also found a correlation between FGF-23
levels and survival time, with cats with an FGF-23 level below 700 pg/mL
having a median survival time of 577 days, compared to cats with an FGF-23
level of 3000-10000 pg/mL surviving a median of 277 days. Cats with a
level over 10000 pg/mL had a median survival time of only 38 days.
TREATING YOUR CAT WITHOUT VETERINARY ADVICE CAN BE
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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