Pathophysiology

Chronic kidney disease

Chronic kidney disease (also known as chronic renal disease) can arise from progression of acute renal failure or congenital or familial diseases, or as the result of acquired conditions affecting glomerulotubular function that have developed over a period of months or years. The most common underlying histopathology associated with chronic kidney disease in cats is tubulointerstitial nephritis. A primary cause is often not identified in cases of CKD, however the associated lesions are irreversible and typically progressive. Remaining intact nephrons undergo a compensatory hypertrophy in order to maintain function. The maladaptive mechanisms that occur as a result of nephron damage further contribute to the progressive decline in kidney function. Among the homoeostatic derangements that may contribute to further progression are mineral imbalance, for example phosphorus retention and secondary hyperparathyroidism, and renal hypertension. Although no treatment can repair irreversible renal lesions, the clinical consequences of reduced renal function can be minimised by appropriate medical management.

Diagnosis

Due to the tremendous reserve capacity of the kidneys, abnormalities in renal function will not be detected until 75% functional capacity is lost. Urinalysis results in conjunction with serum biochemistry values and blood counts are important in establishing a diagnosis of renal insufficiency. The ability of the kidney to reabsorb water from the tubules is reflected by urine specific gravity (USG). Normal cats have concentrated urine, with a specific gravity of > 1.040. Therefore, all cats with USG < 1.035 – 1.040 should be evaluated for kidney dysfunction. Early changes in urine concentrating ability may be the first indication that kidney function is compromised. Therefore annual evaluations of urine specific gravity and body weight are recommended in middle-aged to older cats to detect kidney disease as early as possible. Biochemical changes associated with kidney disease included elevated serum creatinine and blood urea nitrogen (BUN), or azotemia. Azotemia refers to the accumulation of nitrogenous wastes in the blood as a result of decreased glomerular filtration. Additional findings with diagnostic testing and examination may include:

  • Elevated phosphorus
  • Hypokalaemia
  • Anaemia
  • Hypertension
  • Abnormal acid-base status
  • Abnormal size of kidneys on palpation or radiography

 

Clinical signs

  • Dehydration
  • Weight loss
  • Decreased appetit
  • Nausea and vomiting
  • Polyuria/Polydipsia (PU/PD)
  • Lethargy
  • Poor coat condition

Clinical signs are often not evident until 75–80% of the nephrons are non-functional. Routine geriatric screening can help to detect early subtle changes in urinalysis, body weight and blood parameters, facilitating timely intervention.

Staging of kidney disease

The International Renal Interest Society (IRIS) has developed a classification system that distinguishes clinical stages of chronic kidney disease.  These stages correspond to progressive decreases in renal function, as reflected by decreasing glomerular filtration rate and increasing serum creatinine levels.

Staging of CKD is helpful in guiding appropriate empirical management and monitoring of kidney disease for each individual patient.

Staging of kidney disease

The International Renal Interest Society (IRIS) has developed a classification system that distinguishes clinical stages of chronic kidney disease.  These stages correspond to progressive decreases in renal function, as reflected by decreasing glomerular filtration rate and increasing serum creatinine levels.

Staging of CKD is helpful in guiding appropriate empirical management and monitoring of kidney disease for each individual patient.

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Nephron

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Cats with CKD can
survive for months
or years with a good
quality of life with appropriate management