Diagnosing Chronic Kidney Disease
Chronic kidney disease (CKD) is a common clinical diagnosis in middle-aged to geriatric cats and dogs that may significantly
affect the quality of life of both the patients and their owners. Although "old age" is not a disease, it is a time when many
diseases are more likely to occur, often concurrently. Early disease detection of disease conditions allows earlier intervention
and more successful outcomes once treatment has been initiated. Routine monitoring is also helpful to monitor therapy, follow
trends and identify any emerging conditions.
The concept of senior wellness exams should be thoroughly explained to clients to increase compliance. Clients need to be
educated about the definition of a senior pet and the benefits of detecting disease conditions early. Many pets in the early
stages of kidney disease may be asymptomatic, or they may show subtle, non-localized clinical signs often mistaken for age-related
changes by owners. Detecting CKD in the early stages is important so that appropriate therapeutic measures may be instituted
to minimize the progression of disease and delay the onset of uremia.
The diagnosis of CKD requires a very thorough medical history from the owner in addition to a physical exam and laboratory
findings. Owners may report increased thirst, increase urination or accidents in the house. Gradual weight loss, selective
appetite, deteriorating haircoat, may all be signs of CKD as well. Physical exam findings of poor body condition, poor haircoat,
small kidneys, also indicate chronicity. Many laboratory findings are not that helpful in distinguishing acute from chronic
kidney disease, but there are some subtle differences that do occur. For example, a non-regenerative (hypoproliferative) anemia
may be found with chronic kidney disease.
The laboratory diagnosis of CKD is based on demonstrating azotemia (elevated BUN and creatinine) concurrently with inadequately
concentrated urine. In most cases, urine specific gravity values less than 1.030 in dogs and less than 1.035 in cats in an
azotemic patient strongly suggests the diagnosis of primary renal failure. It is important to note that animals with kidney
disease do not typically have urine specific gravities less than 1.006. Values below this specific gravity indicate urine-diluting
capacity, which requires functional kidneys.
Management of CKD
Conservative medical management of CKD consists mostly of supportive and symptomatic therapy. The goal is to correct or improve
deficits and excesses in fluid, electrolyte, acid-base, endocrine, and nutritional balance. Minimizing these changes will
hopefully reduce clinical signs, improve the patients' quality of life and slow the progression of the disease.
Dietary modifications in CKD
Diet therapy has been the cornerstone in the management of canine and feline chronic kidney disease (CKD) for decades. In
the past, the emphasis has been on reducing the protein content of the diets. Although protein content continues to play an
important role in diet formulation, other diet modifications are also important in managing patients with kidney disease.
Compared to adult maintenance diets, diets formulated specifically for dogs and cats with chronic kidney disease typically
have reduced protein, phosphorus, and sodium content; increased potassium, B-vitamin content and caloric density; a neutral
effect on acid-base balance; and an increased omega-3/omega-6 polyunsaturated fatty acid (PUFA) ratio.
Protein
Although the ideal quantity of protein to feed dogs and cats with CKD remains unresolved, a general consensus of opinion supports
the fact that reducing protein intake improves clinical signs in animals with advanced kidney disease. Many of the uremic
toxins are actually by=products of protein metabolism. When not excessive, limiting protein intake does not appear to have
any adverse effects, and it may be easier to initiate treatment with renal diets before the onset of clinical signs of uremia.
In addition, protein restriction may delay onset of clinical signs of uremia as renal disease progresses.
Phosphorous
Renal diets are limited in phosphorus content as patients with kidney disease are not able to clear phosphorous from their
bodies readily. The increase in serum phosphorous leads to problems with calcium and parathyroid hormone metabolism as well;
a syndrome known as renal secondary hyperparathyroidism. Eventually this may lead to bone loss, and mineralization of the
kidneys and other organs. Dietary phosphorus restriction has been shown to enhance survival and a slow decline in renal function
in dogs with induced renal failure. In cats, dietary phosphorus restriction has been shown to limit renal mineralization.
Because protein is a major source for phosphate, it is usually necessary to limit dietary protein to limit diet phosphate
content.
