Download Chronic Renal Failure in the Cat Chronic renal failure (CRF) in

Chronic Renal Failure in the Cat
Chronic renal failure (CRF) in cats is a common presentation in small animal practice. As it is a
disease of older cats there is often co-morbid disease which may affect all aspects of diagnosis
and treatment. Significant advances in our understanding, classification and treatment of this
disease has occurred over the last 15-20 years. These notes will cover
1. The common differential diagnoses of chronic renal failure
2. Definitions of terms used in CRF patients
3. The IRIS classification system for CRF in cats
4. Electrolytes and CRF
5. Treatment tips for cats with CRF
6. Notes on the interaction between CRF and hyperthyroidism
1. Clinical Signs
The most common clinical signs of CRF are weight loss, polyuria/polydipsia and gastrointestinal
signs (primarily vomiting and anorexia). The common differential diagnoses of these signs are
given below:
Weight loss

Chronic renal failure (CRF)

Hyperthyroidism

Diabetes mellitus

Liver disease

Cardiac disease

Poor quality or insufficient diet

Gastrointestinal disease leading to malassimilation or malabsorption e.g. inflammatory
bowel disease, alimentary lymphoma

Hyperadrenocorticism (80% cats have a secondary diabetes mellitus)

Exocrine pancreatic insufficiency

Neoplasia
Polyuria/Polydipsia (PU/PD)
PU/PD is a common presenting sign for many diseases of geriatric cats. Common differential
diagnoses for PU/PD in a geriatric cat include

Chronic renal failure (CRF)

Diabetes Mellitus (DM)

Hyperthyroidism

Liver disease

(Hyperadrenocorticism – secondary DM in 80% cases)
CRF and hyperthyroidism occur concurrently in a significant number of geriatric cats. It is
important to ascertain as much information as possible about a cats renal function before
initiating therapy for hyperthyroidism (see later)
Gastrointestinal signs
Gastrointestinal signs are a common presentation for geriatric cats to the veterinary surgery.
Vomiting is often reported more frequently than diarrhoea and inappetance/anorexia is
commonplace in many complaints.
Differential diagnoses for vomiting in an older cat include:



Primary gastrointestinal disease
o
Inflammatory bowel disease
o
Neoplasia
o
(Infection)
Diseases of organs that affect the normal digestive/absorptive processes
o
Liver disease
o
Pancreatic disease
o
Peritonitis
Non- GI disease
o
Endocrinopathy
o
Toxins
o
Miscellaneous e.g. chronic renal failure, Feline Infectious Peritonitis, congestive
heart failure
Differential diagnoses for inappetance/anorexia
o
Poor quality or insufficient diet
o
Food aversion
o
Oral cavity disease e.g. dental disease, oral neoplasia, trauma, foreign body
o
Chronic renal failure
o
Gastrointestinal, liver and pancreatic disease
o
Neurological disease
o
Behavioural problem
2. Definitions
Before you make a definitive diagnosis of renal failure, whether it is acute or chronic in a patient
it is important to understand some of the definitions we use to ensure that you get the diagnosis
right. Cats with raised urea and creatinine provide a significant diagnostic challenge to the
veterinary clinician. Elevations in urea and creatinine do not necessarily indicate renal
dysfunction. The levels should never be interpreted without a fresh urine sample, and an
accurate urine specific gravity.
Definitions
Azoteamia = raised blood urea and/or creatinine
Azoteamia can be classified in 3 different ways:
Pre-renal - any process that decreases renal blood flow e.g. dehydration, hypovoleamia
Renal – any renal disease which decreases GFR e.g. chronic interstitial nephritis
Post-renal – any disease that causes decreased excretion after the nephron e.g. urinary
obstruction
It is important to distinguish between the 3 forms of azoteamia when faced with a patient
with raised blood urea and/or creatinine (see table 1)
Ureamia = ‘urinary constituents in blood’, indicates renal failure and associated clinical
signs
Blood urea can be raised due to:

Pre-renal factors – e.g. high protein meal (GI bleed), dehydration etc

Renal disease

Post – renal factors e.g. urinary obstruction

Some drugs – e.g. corticosteroids
Blood urea can be decreased due to:

Decreased production – e.g. liver failure, urea cycle disorders

Increases excretion – e.g. diabetes insipidus
Blood creatinine can be increased due to:

Decreased GFR (pre-renal or renal)

(myocyte damage)
Decreased blood creatinine is not clinically significant.
Table 1 – differentiating the 3 forms of azotaemia
Pre-renal
Renal
Urine specific
Urine
Urine
History/clinical
Response to
gravity
volume
sediment
signs
fluid therapy
>1.035
Decreased No evidence of
Shock, dehydration,
Rapid and
inflammation
haemorrhage
dramatic
Usually
Evidence of
Other blood
Slow
increased
inflammation in
anormalities
ARF
suggestive of
1.007 – 1.025
ARF/CRF
Post –renal
<1.007
Decreased
-
Dysuria,
Variable
uroabdomen,
obstructed bladder
3. The IRIS classification system for CRF in cats
The international renal interest society now has a set of guidelines for staging CRF. This
differentiates renal disease (e.g. polycystic kidney disease with no renal insufficiency), from
renal insufficiency from renal disease. All levels of disease are staged and this can be related to
an extent to prognosis. The stages are based on serum creatinine concentrations and
recognised that the relationship between renal disease and creatinine is not linear. It must be
remembered that the IRIS stages have different criteria for dogs and cats. The IRIS stages can
only be applied to animals that are in the stable stages of CRF, it cannot be used to assess a
cat that presents in an acute crisis... In this situation it is advised that you stabilise the patient
before classifying it using the IRIS system.
www.iris-kidney.com
The stages are:

I – early renal disease: creatinine <140µmol/l or < 1.6 mg/dl

Late I – early II – renal insufficiency: creatinine 140-249 µmol/l or 1.6-2.8 mg/dl

Late II – early III – early renal failure: creatinine 250-439µmol/l or 2.9-5.0 mg/dl

Late III – early IV – uraemic renal failure: creatinine >440 µmol/l or >5.0 mg/dl

Late IV – end-stage renal failure
The creatinine levels assigned to each IRIS stage are:
Stage I - creatinine <140µmol/l or < 1.6 mg/dl
Stage II - creatinine 140-249 µmol/l or 1.6-2.8 mg/dl
Stage III - creatinine 250-439µmol/l or 2.9-5.0 mg/dl
Stage IV - creatinine >440 µmol/l or >5.0 mg/dl
The disease can then be sub-staged depending on the degree of proteinuria and systolic blood
pressure:
Blood pressure
Interpretation
Urine
Interpretation
protein:creatinine ratio
<150mmHg
Minimal risk of end
<0.2
Non-proteinuric
0.2-0.4
Borderline proteinuric
>0.4
Proteinuric
organ damage
150-159mmHg
Low risk of end organ
damage
160-179mmHg
Moderate risk of end
organ damage
≥ 180 mmHg
High risk of end organ
damage
4. Electrolytes and CRF
Once a diagnosis of CRF (azotaemia and urine specific gravity <1.025) has been made and the
IRIS stage calculated it is recommended to measure the cats electrolytes particularly phosphate
and potassium.
Phosphate
A significant number of CRF cats will be hyperphosphateamic,
Differential diagnoses of elevated phosphorous include:

Renal failure

Hyperthyroidism

Vitamin D toxicity

(Addisons)
It is very important to try to correct the level of hyperphosphataemia as it has significant effects
on appetite and demeanour. Persistently elevated phosphorous can also interfere with normal
calcium metabolism and lead to elevations in parathyroid hormone which is thought to have
deleterious effects on the body.
Potassium.
Potassium levels are normally within the reference range or low in CRF cats. However in a few
individuals mild hyperkalaemia is present. The degree of hypokalaemia can vary but can be
profound enough to cause significant muscle weakness. In most situations the extent of
hypokalaemia is not this severe but it is very important to bring the potassium back within the
normal range as it will have significant effects on appetite and demeanour.
Other causes of hypokalaemia include:

Hyperthyroidism

Fluid therapy

Frusemide therapy

Vomiting and diarrhoea

Idiopathic hypokalaemia

Alkalosis

Hyperaldosteronism (Conn’s disease)
Chronic renal failure patients are often mild to moderately acidotic; if you have the facility
measuring the acid-base balance of a cat it is advisable to monitor their status regularly. In most
cases the acidosis will correct itself as the other metabolic derangements are returned to
normal.
5. Treatment tips for cats with CRF
There are many different therapeutic options for cats with CRF. Not every cat will require the
same treatment and the therapeutics you should choose should be based on your clinical
findings. Initially it is important to correct the electrolyte disturbances, dehydration,
gastrointestinal derangements and uraemia (if present). Hypertension and anaemia are other
potential complications that need stabilisation.
Don’t forget that:

Cats with CRF have a progressive disease though it is impossible to predict the rate at
which a cat will deteriorate. It is vital to educate the owner about their cats’ condition and
gauge their commitment towards treating their cat. www.catprofession.com

Prescription diets which are low in protein, phosphorous and sodium, and high in
calories, potassium and B vitamins, are the mainstay of treatment of CRF patients and
are shown to improve survival.

The water intake of the cat needs to be increased so multiple sources of water should be
available and wet diets may be preferable to dry ones. Some owners are very capable of
intermittently administering subcutaneous fluids at home. Semi-permanent indwelling
subcutaneous catheters have now been produced to facilitate this more easily.

Cats are obligate carnivores and it is essential that they have a constant source of
protein. Cats with CRF are often in a negative energy balance and it is important to get
the cat eating again as soon as possible. Ideally call cats with CRF should ultimately be
on a protein restricted diet but introduce them slowly. Initially get the cat eating
something and it hasn’t eaten for over 3 days then assisted (tube) feeding is required.

Some cats may require phosphate binders to solve their hyperphosphataemia even if
they are on a prescription renal diet.

Some cats will need extra potassium supplements to bring their potassium back within
the normal range.

Not at CRF cats need an angiotensin converting enzyme inhibitor (ACE inhibitor), the
author would use them in proteinuric cats (UPC > 0.4) and as a2nd line treatment for
hypertensive cats. Some veterinarians report an increased quality of life in cats on ACE
inhibitors so this may be an indication for these drugs. ONLY use ACE inhibitors during
the stable stages of CRF not in acute presentations of the disease.

Calcitriol therapy to reduce parathyroid hormone levels is controversial. If you use
calcitirol therapy then monitor the blood calcium closely as hypercalcaemia can have
very deleterious effects.

Erythropoietin can be useful for chronic severe anaemias
6. Notes on the interaction between CRF and hyperthyroidism
Geriatric cats with concurrent hyperthyroidism and CRF present a diagnostic and therapeutic
challenge.
Non-thyroidal illnesses such as CRF can falsely lower TT4 masking hyperthyroidism; conversely
hyperthyroidism can increase GFR masking CRF. Additionally the weight loss and decreased
muscle mass seen in hyperthyroid cats can lower serum creatinine levels masking the signs of
CRF further.
Hyperthyroidism can improve renal function in some patients by increasing renal blood flow and
therefore perfusion and thus maintaining GFR within normal limits. However it is also thought
that hyperthyroidism can exacerbate CRF particularly in the presence of systemic hypertension.
If the autoregulation systems within the failing kidney are inadequate, the systemic hypertension
is transmitted across the glomeruli causing intraglomerular hypertension and hyperfiltration.
These factors are known to cause glomerular sclerosis and promote the progression of CRF.
This means hyperthyroidism can be beneficial in patients with CRF and also damaging. Treating
a cat for hyperthyroidism can ‘unmask’ subclinical CRF and cause a marked decline in the
clinical condition. So how should these patients be managed?

It is very important to assess renal function in all hyperthyroid patients prior to therapy.
o
Normal blood urea and creatinine does not necessarily mean that there is no
renal disease. These are very insensitive markers of GFR but in veterinary
practice more accurate methods of measuring GFR are not available.
o
Urine specific gravity should be measured in all hyperthyroid cats.
o
Patients with a USG < 1.035 should be considered as potentially having
underlying renal insufficiency.
o
Normal USG in a hyperthyroid cat does not confirm normal renal function once
the cat is euthyroid

Ideally all hyperthyroid cats should be treated with oral therapy in the early stages of
stabilisation
o
This enables the renal function to be monitored (via blood sampling and
urinalysis) whilst the thyroid level is brought to within normal limits.
o
Oral medication for hyperthyroidism is completely reversible.
Following stabilisation with medical therapy:

If a euthyroid cat has normal serum urea and creatinine, more permanent methods of
treatment can be considered e.g. radioactive iodine or surgery.

If a euthyroid cat has raised serum urea and/or creatinine and/or decreased USG, this
would suggest underlying renal insufficiency.
o
This means that permanent treatment for hyperthyroidism is not appropriate.
o
A balance between the hyperthyroidism and CRF needs to be found in these
patients.
o
The dose of methimazole can be titrated to the maximum dose that helps combat
the effects of the hyperthyroidism without compromising renal function. These
patients must be monitored very closely for a deterioration in either disease
process.
If a hyperthyroid cat, with possible underlying CRF is impossible to medicate then it is prudent to
discuss with the owner the possible detrimental effects of more permanent treatment.
Cats with CRF should be suitably managed for this condition as well as the hyperthyroidism.