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Chronic Kidney Failure
Chronic renal failure (CRF) is long-standing kidney damage and dysfunction manifested by dilute urine and build-up of waste products (urea, creatinine, phosphorus) in the body.
The kidneys three main functions are:
- filtrating toxins (BUN, creatinine and phosphorus) out of the blood into the urine, but saving the nutrients in the blood such as proteins and vitamins
- concentrating the urine and thereby preventing dehydration
- the production of erythropoetin, a hormone that stimulates red blood cell production
Consequently when renal tissue is damaged, the clinical signs and problems that result are linked to the compromise of these functions.
It is common in older dogs but is also sadly seen in younger ones too.
In many cases the original cause is never found.
Identifiable causes include kidney infections and stones, incomplete recovery from acute renal failure and diseases of the glomerulus such as glomerulonephritis or protein-losing nephropathy. In younger dogs, congenital kidney disease such as kidney dysplasia may be the cause.
CRF may be detected on routine blood and urine tests prior to the onset of signs and diagnosis at this early stage allows treatments to be initiated that may slow further progression.
Early clinical signs include increased drinking and urination (PD/PU) weight loss and reduced appetite.
In later stages vomiting, dehydration, lethargy and bad (uraemic) breath are seen.
Initially full biochemistry, electrolytes and haematology are performed on a blood sample, looking for build-up of waste products indicating poor renal function.
Urine is tested for protein (lost by the kidneys in CRF) and dilution (determining the ability of the kidneys to concentrate the urine and thereby conserve water)
Additional tests may include urine culture to screen for underlying infection, radiographs and ultrasonography, and blood pressure measurement. In some cases a kidney biopsy may be indicated.
Management revolves around supporting the remaining kidney function, reducing the load on them and also treating the patient for the resultant deficiencies.
Currently no treatments are available to reverse CRF, and the goals are to slow progression and treat the clinical signs, thereby maintaining quality of life.
A special diet with less protein and phosphorus is the most effective measure and can double lifespan in CRF dogs compared to those still on normal diets.
Control of phosphorus levels in particular are important and if diet alone is not sufficient, phosphorus binders such as aluminium hydroxide can be added to the food.
If chronic dehydration is present regular injections of fluids under the skin (subcutaneous fluids) may help with frequency varying from twice daily to twice weekly, and can be done by the owner at home.
High blood pressure (hypertension) can be controlled with various drugs, as can a raised calcium level.
Potassium supplementation and erythropoietin injections to stimulate red blood cell production may also be needed, although, unlike cats, dogs rarely develop low potassium levels from CRF.
Follow Up Care and Prognosis
Frequency of further tests depends on the severity of the CRF present and can range from monthly in severe cases to every 6 months in early, stable cases.
CRF is a progressive disease but rate of deterioration is highly variable. Whilst lifespan is impossible to predict, animals diagnosed with early CRF have an average lifespan of 3 years whilst those with advanced disease may succumb within weeks to months.