7 Mar 2016
Samantha Taylor focuses on how to diagnose chronic kidney disease in cats so they can be treated at an earlier stage of diagnosis (part 1/2).
Samantha Taylor
Job Title
Figure 2. Systolic blood pressure measurement should be part of the clinical examination of older cats.
Chronic kidney disease (CKD) is a common diagnosis in cats presented to first opinion practices and renal disease is the most common cause of mortality in cats of more than five years of age (O’Neill et al, 2015).
General practitioners are familiar with the management of this condition, but given the prevalence and research, the treatment of CKD is worthy of review to ensure we are doing all we can to maximise the length and quality of life in affected cats.
The International Society of Feline Medicine (ISFM) has produced international guidelines on the management of CKD and the Journal of Feline Medicine and Surgery has published guidelines offering a consensus of opinion from international experts (Sparkes et al, 2016).
This article will discuss developments in diagnosis, what treatments make a difference to affected cats and how to apply them optimally in a busy, first opinion practice. Part two will cover the management of complications of CKD, including proteinuria and urinary tract infections.
Classic clinical signs of CKD include polyuria and polydipsia, inappetence, vomiting and weight loss. However, as a species, cats are masters of hiding disease and owners may attribute vague and non-specific signs to ageing.
The challenge is diagnosing CKD before a cat is in poor clinical condition and the disease is advanced. This means more opportunities to intervene and prolong the cat’s life, as well as improving the quality of life. As a practice, can you review how you could identify and test older cats for CKD, and other common diseases associated with ageing, to allow an early diagnosis and avoid missed treatment opportunities?
A diagnosis of CKD is made in the majority of cases when azotaemia is detected in combination with a reduced urine specific gravity (USG; less than 1.035).
However, creatinine and urea are affected by non-renal factors (such as hydration, muscle mass and feeding) and should be interpreted accordingly. They are also insensitive indicators of a reduced glomerular filtration rate (GFR), increasing after the loss of around 75% of renal function.
Measurement of GFR is routine in humans, but not performed as simply in cats and rarely indicated. In some cases, early in the course of the disease, a loss of concentrating ability may occur in advance of the development of azotaemia and cats will occasionally maintain concentrating ability despite having renal disease.
Whatever their limitations, none of these abnormalities will be detected if you are not looking for them. Early diagnosis is desirable to allow interventions to prevent further renal damage, slow progression and manage complications of CKD.
Once a diagnosis of CKD is made, the cat should be staged according to the International Renal Interest Society (IRIS) staging system.
SDMA is a methylated arginine amino acid produced as a result of proteolysis. It is excreted by the kidneys and correlates with GFR in cats (Braff et al, 2014). Studies have demonstrated its utility as a biomarker for CKD, increasing earlier than creatinine and not affected by muscle mass (Hall et al, 2014).
As SDMA correlates with GFR, it increases in cases with prerenal and postrenal azotaemia, and further study is required to assess its utility; for example, in cases of acute kidney injury. It is worth considering whether this test could be used to assess older cats for CKD prior to the development of azotaemia in your clinic, perhaps pre-anaesthesia or in senior cat clinics.
Importantly, it can be used to identify cats that should be monitored for the development of CKD.
IRIS has guidance on the interpretation of SDMA results summarised as:
For more information, visit www.iris-kidney.com
Once a diagnosis of CKD is made, the goals of treatment are to prevent progression of the renal disease and maintain a good quality of life by minimising complications and clinical signs.
Initial work-up for treatable underlying causes is recommended (such as lymphoma, pyelonephritis and urolithiasis), but the majority of cats will have chronic tubulointerstitial nephritis with no known aetiology.
Renal diets are restricted in protein and phosphate, supplemented with potassium, B vitamins and omega-3 fatty acids. Certainly, it is simple to send a client home with a bag of renal prescription diet, but communicating to clients the importance of a renal diet in slowing the progression of CKD is vital to compliance.
To many vets and owners, a diet is not seen as a “treatment”, when it has been shown to prolong life and reduce episodes of uraemia in cats with CKD (Elliot et al, 2000; Ross et al, 2006).
Despite this compelling evidence, a recent study of 1,089 cats with CKD showed only 51% were fed a veterinary therapeutic diet as some component of a diet (Markovich et al, 2015). In the same study, 43% of owners reported their cats had an abnormal appetite. Are we missing an opportunity to maximise use of the best therapy we have (Figure 4)?
The way a diet is introduced can make a big difference to acceptance by the cat. Panel 1 lists ways to smooth the transition to a renal diet. Food is likely more expensive than owners’ usual brands, and they need to understand why.
Many owners would be happier paying for tablets than a bag of prescription diet, but CKD is one disease where we need to explain the difference a diet can make. We also need to tell them how much they should be feeding and monitor the cat’s intake.
Do owners leave your practice knowing how much of a diet in grams their cat should be eating? Do you follow-up later with a telephone call or email to see how the transition is going and if you can offer more advice? There are other ways to support the client here and, given the importance of diet, this is worthy of thought.
The benefits of a renal diet do not mean maintenance of calorie requirements comes second. If a cat refuses the diet, or eats an inadequate amount despite efforts described in Panel 1, then feeding a part of the diet may still be helpful. Senior diets often have reduced protein and phosphate content, but blood phosphate should be monitored and phosphate binders used with the diet, if necessary.
ISFM guidelines recommend introducing a renal diet as early as possible and to IRIS stage 2 cats. Early intervention means a cat’s appetite will be better and a diet better accepted. Plus, the earlier renal secondary hyperparathyroidism can be mitigated, the better.
CKD is a common condition affecting older cats. Earlier diagnosis is preferable to afford more opportunities to intervene and prolong the life of these cats.
Strategies to encourage clients to attend the clinic with their, seemingly healthy, older cats should be devised and implemented. Clients should be well informed and supported as they change their cat’s diet. The next article in this series will discuss other ways to manage cats with CKD.
This panel offers guidance on how to transition a cat with CKD to a prescription renal diet.
