#drferox

Let’s start from the beginning: what is chronic kidney disease?

Chronic kidney disease (CKD) is a progressive disease of lost renal function. It’s a very common cause of death in cat’s over 14 years old. Kittens are born with 100% function of their kidneys, but as they age, function slowly decreases leading to clinical signs. This can be distinguished from acute kidney injury (AKI) by multiple factors, but the main difference is that CKD is an almost inevitable consequence of age, while AKI can happen at any age, and usually has an inciting factor like trauma or a bad infection.

Renal disease is classified into 4 stages, IRIS stages, based on bloodwork levels of 3 waste products: SDMA, BUN, and creatinine.

Stage 1 & 2: often no clinical signs, very early to early renal disease

Stage 3: can see polyuria and polydipsia (increased thirst and urination), decreased appetite, weight loss, and lethargy as creatinine rises in the blood

Stage 4: usually very sick! Poor to absent appetite, rapid weight loss, very lethargic and anti-social, and often extremely dehydrated

Protein requirements of cats

Cats are obligate carnivores, unlike dogs which are facultative carnivores, and this is reflected in their protein requirements! Cats generally require approximately 34% protein or more on a dry matter basis (I’ll touch on dry matter vs crude protein that at the end) to maintain lean muscle mass, or they begin to metabolize it for energy (LaFlamme & Hannah, 2013; Salauq, 2016).

As cats age, they need more protein in their diet! As cats age (greater than 12 years old), the absorptive abilities of their digestive system wane so they need an almost overload of protein to help their gut absorb enough: at lowest 40% protein and up to 50% protein. Due to the decreased absorption they also have an increased fat requirement (>20%), especially omega fatty acids, and supplemental B vitamins, especially B12 are recommended (Sparkes, 2011; LaFlamme & Gunn-Moore, 2014).

So what’s the controversy?

In renal disease, the kidneys are less able to filter out waste products the body makes, leading them to overload the body and make the animal sick. Many of these waste products, including BUN and creatinine, are created from the breakdown of proteins: either in muscle or in food. (Fun fact: intensely muscled horses may have high creatinine just due to the immense amount of muscle they have, while conversely very skinny, atrophied animals will have lower). Protein also contains high levels of phosphorus, which can be detrimental to cats with kidney disease.

The main thought behind the low-protein renal diets is to not overload the animal’s kidneys with excess protein and make them sicker.

However, Dr Gary Norsworthy, one of the leading feline specialists, recommends a high protein diet to all cats but those in the latest stages of CKD. Why?

Hyperthyroidism, diabetes, and GI disease, 3 of the most common diseases in senior cats, can all lead to muscle wasting

Starting cats out with a restricted protein diet that may have these diseases in hopes of preventing/stalling CKD would likely only cause even further atrophy, especially since senior cats already have decreased protein absorption.

The important clinical goals of managing early (IRIS 1 & 2) CKD are:

Maintain hydration! Kidneys love water, and keeping kitties hydrated can prevent or slow degradation of the kidneys. - water fountains, wet food, Purina Hydracare, IV/sub-Q fluids 

Maintain normal phosphorus levels. Hyperphosphatemia directly correlates to an increased mortality in both human and feline patients with CKD - low phosphate diets, phosphate binders

Control other risk factors, like hypertension and hypokalemia

Very high blood pressures can further damage the kidneys (like “spraying a fire hose on a delicate filter”)

If you control these factors, high protein should not be an issue for cats with early CKD

Norsworthy is generally against traditional renal diets in cats, which often have 23-27% protein, below the threshold of muscle wasting in cats! (As a note: Hill’s K/D has only slightly lower protein in it than their standard adult food: 30% in K/D, 34% in K/D early care, and 36% in adult. Purina NF is still following a more restricted protein diet at 26%, but their NF early care is 34%)

Restricted protein will lower BUN and creatinine, which may be giving clinicians a false sense of security that the renal disease has been controlled (also lowers phosphorus, but that can usually be controlled without lowering protein)

Another fun fact: cats on high protein diets (Like Dr Elsey’s which has 59% protein) will often have an above-threshold BUN, but is not an indicator of renal function! Just their diet.

There’s also little evidence to support protein restriction in cats! Many studies on low protein are extrapolated out of other species, and cats aren’t small dogs, or small humans. They need their own studies!

In advanced kidney disease (IRIS 3 & 4), the greatest challenge to maintaining quality of life in these cats is food intake. Remember, the increased severity of kidney disease often leads to loss of appetite and subsequent weight loss, and these poor cats end up wasting away to skin and bones. Increased weight loss and muscle atrophy correlates to a shorter lifespan in senior cats (Sherk, “Skinny Old Cats”). However, cats prefer eating high protein diets over low protein! So to keep their weight and muscle from decreasing, a higher protein, increased palatability diet is recommended.

What about in severe renal disease cases?

Norsworthy recommends in IRIS 4 cats with uremia (high BUN) and hyperphosphatemia that cannot be controlled by other means, only then should protein be restricted, and only to 30-38% protein, and only if the cat will eat enough to meet caloric needs. 

I finished up some more artwork for @drferox recently! She’s a fabulous vet and storyteller, and everyone who likes animals (extant, extinct, and mythological) and real-life tales from the veterinary world should check out her blog.

drferox said: I will be thoroughly unprepared if that ever happens. If you studied at unimelb you might have been in the same year level as my recent grad vet.

(holy shit, hi!)

I studied in Adelaide, so nope on that count. But I’ve gotten to know a few unimelb graduates in my year equivalent and below through another recent grad at my clinic.

Oh.

My.

Doc.

Basically I'm a huge @drferox fan and could not believe my eyes when I saw this. As I see it, there are 3 things to process here:

1) Dr Ferox has seen my art

2) Dr Ferox has not just seen, but also appreciated my art

3) On some small level, Dr Ferox is aware of my existence

So clearly a lot to process here. I've been a huge fan for several years, because the posts of Dr Ferox have provided entertainment, education, inspiration, and encouragement throughout my vet school journey. This queen of tumblr vets and sass is basically an amazing person whose content impacts me in more ways than I could fit in one post.

Thank you @drferox !! I LOVE THEM SO MUCH

(Also, I'm in the US so rest assured, they have shipped and are being received by happy overseas vetlings like me!)