I have no personal experience with kidney disease in dogs, but I sometimes
get asked about it, so below I explain the IRIS staging system for CKD in
dogs and provide links to further information and support groups.
IRIS Staging System
When your dog is first diagnosed, you may immediatrely
wonder how serious it is. Many vets now take the test results and categorise them
according to the system provided by the
International Renal Interest Society. This divides
CKD into four stages; so if your vet tells you, for
example, that your dog is in Stage 2, s/he is probably referring to the
IRIS staging system.
Staging should only occur after diagnosis. Before
making a firm diagnosis of CKD, two blood test readings from a stable dog 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 dog.
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 dog 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.
IRIS staging of CKD
(2019) International Renal Interest Society) looks at three things in this order:
blood tests
proteinuria
(levels of protein in the urine)
hypertension
(high blood pressure)
IRIS Staging System: Blood Tests
The IRIS staging system begins by looking at the dog's
creatinine levels
(creatinine is a measure of kidney function). 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 1.4
Creatinine below 125
0 -
65%
Stage 2
Creatinine
between
1.4 and 2.8
Creatinine between
125 and 250
66 -
75%
Stage 3
Creatinine
between
2.9 and 5.0
Creatinine
between
251 and 440
76 -
90%
Stage 4
Creatinine over 5.0
Creatinine over 440
Over 90%
Obviously, not every dog with creatinine below 1.4 mg/dl
(US) or below 125 µmol/L (international) has CKD! The problem is that when measuring creatinine,
you cannot detect
CKD until at least 66% of function has been lost, because before that there
are usually no symptoms (see
What Happens in CKD).
Therefore for dogs in Stage 1 who do 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).
IRIS Staging: SDMA
The staging system 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
1.4 mg/dl
Below 125 µmol/L
Below
18
If SDMA is increasing or is consisently above 14, CKD may be
present.
Stage 2
1.4 - 2.8 mg/dl
125 - 250 µmol/L
18 - 35
This is considered by IRIS to be mildly increased.
Stage 3
2.9 - 5.0 mg/dl
251 - 440
µmol/L
36
- 54
Stage 4
Over 5 mg/dl
Over 440 µmol/L
Over 54
For dogs with persistently elevated SDMA readings,
IRIS staging of CKD
(2019) International Renal Interest Societysuggests changes in the stage of CKD the
dog is deemed to be in as
follows:
Creatinine Level
Current IRIS Staging
Based
on Creatinine Levels
SDMA Measurement
Revised
IRIS
Staging
Below 1.4 mg/dl
Below 125 µmol/L
Stage 1
Over 18
Stage 2
1.4 - 2.8 mg/dl
126 - 249 µmol/L
Stage 2
Over 35
Stage 3
2.9 - 5.0 mg/dl
250 - 440 µmol/L
Stage 3
Over 54
Stage 4
In all cases, two readings in a stable dog (who is not
dehydrated - this can make the numbers look a lot higher than they really
are), ideally
after fasting (though that is not always the best choice for a CKD patient), are required
before making a firm diagnosis of CKD. In practice, most vets will make
the diagnosis based on bloodwork taken once during your initial visit.
IRIS Staging System: Proteinuria
IRIS staging of CKD
(2019) International Renal Interest Society
then recommends sub-staging based
on whether proteinuria
is present.
Healthy
dogs only have tiny amounts of protein in their urine because their
kidneys do not allow the protein to leak through. In CKD dogs, 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 dog has proteinuria is via
the urine protein:creatinine ratio (UPC).
Three urine samples should be collected over a mimimum 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 0.5
Borderline Proteinuric (BP)
Over 0.5
Proteinuric (P)
There is a correlation between the severity of proteinuria in cats and the
prognosis, though I don't know if the same
applies to dogs.
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
Medicine20 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 dog'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 dog's UPC ratio is indeed high, it
may gradually reduce with
treatment.
IRIS Staging System: Hypertension
IRIS staging of CKD (modified 2019)
(2019) 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
BP Substage
Treatment Plan
Under 140
Minimal
Normotension
No treatment necessary
150 - 159
Mild
Borderline 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
Severe
Severe hypertension
Begin or increase blood pressure medications
Some dog breeds, such as sight
hounds, tend to have higher blood pressure naturally. For these breeds,
IRIS recommends using breed-specific reference ranges if possible.
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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