Chronic kidney disease (CKD) is a common problem that affects an estimated 0.5 to 7% of dogs and 1.6 to 20% of cats. Nephron
damage associated with CKD is usually irreversible and can be progressive. Renal failure results when three-quarters or more
of the nephrons of both kidneys are not functioning. Whether the underlying CKD primarily affects glomeruli, tubules, interstitial
tissue, or renal vasculature, irreversible damage to any portion of the nephron renders the entire nephron nonfunctional.
Healing of irreversibly damaged nephrons occurs by replacement fibrosis and therefore a specific etiology is often not determined.
Chronic kidney disease occurs over a period of weeks, months, or years and is an important cause of death in dogs and cats.
It is often not possible to improve renal function in CKD and therefore treatment is aimed at stabilizing renal function.
Importantly, there is increasing evidence that dietary and anti-hypertensive treatments can decrease the progressive nature
of CKD.
Etiology
The cause of canine and feline CKD is usually difficult to determine. Due to the interdependence of the vascular and tubular
components of the nephron, the end point of irreversible glomerular or tubular damage is the same. Morphologic heterogeneity
between nephrons exists in the chronically diseased kidney with changes ranging from severe atrophy to marked hypertrophy.
These histologic changes are not process specific and, therefore, an etiologic diagnosis is frequently not possible. The more
common renal diseases that have been associated with the development of CKD in dogs and cats include glomerulonephritis, amyloidosis,
tubulointerstitial disease, pyelonephritis, nephrolithiasis, polycystic kidney disease, feline infectious peritonitis, leptospirosis
and neoplasia. Progressive diseases that destroy nephrons at a slow rate allow intact nephrons to undergo compensatory hypertrophy
which can delay the onset of renal failure. In these cases, when renal failure finally occurs, the nephron hypertrophy can
no longer maintain adequate renal function and < 25% of the original nephrons are functional. This points out the need for
early diagnosis and intervention.
Staging of Canine and Feline CKD
The International Renal Interest Society (IRIS) was created to advance the scientific understanding of kidney disease in small
animals at the 8th Annual Congress of the European Society of Veterinary Internal Medicine in Vienna, Austria in 1998. Seventeen
independent veterinary nephrologists from eight countries serve on the IRIS Board with the mission of helping practitioners
better diagnose, understand, and treat canine and feline renal disease. The following table was developed by the IRIS Board
as guide to staging feline CKD.
Serum creatinine concentrations must always be interpreted in light of the patient's urine specific gravity and examination
findings in order to rule out pre- and post-renal causes of azotemia. The above stages are further classified by the presence
or absence of proteinuria and systemic hypertension as follows:
Prevalence of Feline CKD
The distribution of staging of 786 cases of CKD in cats was reported by Dr. Jonathan Elliott from the Royal Veterinary college
in London at the 2004 ACVIM Forum as follows: Stage I = 33.3%, Stage II = 37.2%, Stage III = 15.4%, and Stage IV = 14.1%.
Similar data has not yet been determined for dogs.
