Once a dog or cat has lost at least 75% of renal function, they begin to accumulate waste products in their blood (BUN=blood urea nitrogen, creatinine) from protein breakdown and they lose their ability to concentrate their urine. Healthy kidneys make products that regulate blood pressure and stimulate red blood cell production from the bone marrow, so dogs and cats with renal failure can develop high blood pressure and anemia (a low red blood cell count). These patients can also have abnormalities in major blood electrolytes (phosphorus, potassium, calcium).

If the loss of renal function occurs over the course of several months (3 or more), it is considered to be "chronic" (Chronic Renal Failure or CRF). If the insult is sudden in onset (over 1-2 weeks) it is considered to be "acute." In cases of acute renal failure (ARF), some renal function may be restored with early and aggressive intervention and treatment for the underlying cause. Once the process is prolonged, it is generally not possible to reverse the damage that has been done.

A certain subset of dogs (and rarely cats) can develop protein losing nephropathies (PLN) as a result of damage to the glomerulus (a bundle of small blood vessels within the kidney where the blood is initially filtered). This results in a "leaky" filter that allows larger proteins to make their way through the filter and into the urine. Protein losing nephropathies tend to be more severe and rapidly progressive. One of the more common causes of PLN is Lyme disease, particularly in retriever breeds (Golden Retrievers and Labrador Retrievers).

One of the earliest signs of chronic renal failure is drinking more and urinating more. This can occasionally result in urinary accidents inside the house. Once BUN, creatinine and phosphorus reach higher levels in the blood (also called "uremia"), your pet might experience lethargy, weakness, a decreased appetite, weight loss and/or vomiting or diarrhea. There is a characteristic odor to uremic breath so often owners note halitosis.

In cases of acute renal failure, the kidneys might shut down altogether so dogs and cats might not be able to produce urine at all. They become severely ill over the course of hours to days.

How are these conditions diagnosed?

Initial diagnostics for renal failure include a blood chemistry (including BUN, creatinine, electrolytes, proteins, cholesterol, etc), a complete blood count (including red blood cell, white blood cell and platelet counts) and a urinalysis. Further diagnostics to identify an underlying cause or assess the severity of the disease might include a urine culture, a urine protein:creatinine ratio, testing for infectious diseases, testing for potential toxins, a blood pressure measurement, radiographs or an abdominal ultrasound.

Is there anything I can do to prevent it? 

There are a number of different causes of renal failure (see table below). Some are preventable and treatable through avoidance, vaccination or medication.

However, in most cases an underlying cause is never identified.

*    vaccines available

** NSAIDs: non-steroidal anti-inflammatory drugs such as acetaminophen and ibuprofen

*** Bacterial infection of the kidneys

In cases of ARF, treatment is aimed at the underlying cause in order to try to restore renal function and potentially reverse some of the damage. This would include treatment of infectious causes, immune mediated causes or toxins. Once the condition is chronic, the goal is to simply slow the progression of the disease and alleviate clinical signs. Early detection and intervention is the key to optimizing the prognosis for your pet.  

In general, cats tend to respond better than dogs to early intervention for CRF. Research has shown that the most important factor to prolong survival in both dogs and cats with renal failure is to transition them to a low protein, low phosphorus diet. It is crucial to transition them when they are eating well and have a good appetite or they can develop an aversion to the prescription food. Medications might also be added to control phosphorus levels, high blood pressure, and nausea/vomiting or gastrointestinal ulceration.

In the later stages of CRF, many pets benefit from supplemental fluids that can be administered subcutaneously (under the skin). Many owners can be trained to treat their pets in the comfort of their own home. The additional fluids help to maintain hydration and "flush" out some of the toxins in the blood.

Other treatment options that are much less frequently pursued because of the associated risks, quality of life and cost concerns include transfusions, injections to stimulate red blood cell production, dialysis and kidney transplantation (cats).