Chronic kidney disease (CKD) is among the most significant causes of morbidity and mortality in domestic cats. Early diagnosis of CKD allows for intervention in the form of dietary modification, anti-proteinuric medications, blood pressure regulation, and other steps to slow progression and maintain quality of life. Since many cats do not show clinical signs until CKD is quite progressed (IRIS stage 3-4) there is often very little to prompt blood or urine screening.

Previous research has indicated that cats will often lose ~10% of their body weight within the year prior to diagnosis with CKD. It is well established that cats with clinical CKD are often classified as “thin” or “emaciated”.  The cause of this weight loss may be a combination of anorexia, increased energy demand, malabsorption and inflammation.

The purpose of this study was to evaluate the time course of weight loss in cats with CKD before and after diagnosis, and to evaluate the prognostic effect of weight on survival in CKD.  The study design was retrospective in nature and evaluated 569 cats with CKD from 6 veterinary referral practices within the United States. Data collected included the IRIS stage of CKD, date of diagnosis, weight at diagnosis, and weight within the three years prior to diagnosis.

Various data analysis techniques were used to evaluate body weight changes over time, as well as performing a survival and hazards analysis. Median survival time was 17.7 months, with cats in IRIS 1 and 2 surviving longer than cats in IRIS 3 and 4. Older cats also did not survive as long as younger cats.

Interestingly, body weight was associated with survival in cats with CKD in a bimodal fashion. Cats with body weight significantly below the median had an increased risk of death, as the cats that were significantly overweight, forming a “J” shaped curve. Interestingly, cats that were slightly over the median weight had a better survival time than cats of average weight. This “obesity paradox” has been described in humans and dogs, whereby individuals who are slightly overweight fare better in disease states than ideal-weight animals.

Cats experienced an average of 8.9% weight loss in the 12 months prior to diagnosis of CKD. This is very similar to previous studies indicating 10% weight loss. Growth curve analysis suggested that weight loss may begin up to 3 years prior to diagnosis. This weight loss increases in rate after diagnosis.

There were many limitations to this study, including its retrospective nature, lack of information on body conditions core or muscle condition score, lack of standardized treatments, and lack of information on concurrent disease.

Detection of CKD at an earlier stage may allow for quicker and more effective intervention. The development of weight loss prior to clinical diagnosis of kidney disease indicates that a drop in body weight may be an early warning that should prompt further investigation.

The effect of weight on survival in cats with CKD was also shown to be of some prognostic utility. Knowing that cats with normal to slightly high body condition may have better survival when affected by CKD may help veterinarians to adjust the aggressiveness of their therapy and provide meaningful information on prognosis to cat owners. Cats who are underweight at the time of diagnosis may have a poorer prognosis. (MRK)