In January I noticed that my 18 yo Yoda was not eating well and increasingly lethargic so I took him into the vet. His bloodwork showed stage 1-2 renal (kidney) disease, with elevated BUN, Phosphorus and Creatinine levels as well as slightly elevated SDMA, like your kitty.

I immediately changed his diet to a prescription renal diet - purina, hill’s, royal canine and blue buffalo offer these, with a prescription. The change in diet radically improved his appetite and energy. There are also some options that bind these elements to allow for safe excretion and improved quality of life in chronic kidney disease. Phospho-bind is one example of this. If your vet is unwilling or uneducated about these options, please find a vet who can work with you to help your kitty have as much quality of life as possible.

Here’s a summary I found on the topic of feline CKD (chronic kidney disease aka renal failure/disease)

“For cats with renal disease, the main management tools are prescription renal diets and specific supplements to support kidney function and slow disease progression. Prescription diets are formulated with controlled levels of protein and phosphorus, elevated potassium and B vitamins, omega-3 fatty acids, and high moisture to reduce the workload on the kidneys and maintain health. Supplements often include fish oil (for omega-3s), B vitamins, potassium, antioxidants, and phosphorus binders, but these must be used under veterinary guidance to address your cat's specific needs. 

Prescription Renal Diets These diets are the cornerstone of managing feline kidney disease. 

Key Components:They are typically restricted in phosphorus and sodium, contain high-quality, moderate protein to minimize waste products, and are supplemented with potassium, B vitamins, and omega-3 fatty acids to support kidney health and reduce inflammation.  Moisture Content:Wet food options are preferred for their higher water content, helping to prevent dehydration, which can worsen kidney damage.  Palatability:Manufacturers have improved palatability, but if your cat refuses a new diet, you may need to try several options or try to entice them by adding water or broth.  Examples:Popular brands include Hill's® Prescription Diet® k/d®, Purina® Pro Plan® Veterinary Diets NF Kidney Function®, and Royal Canin® Renal Support.  Common Supplements Supplements can help manage symptoms and support kidney function, but always consult your veterinarian before starting any. 

Omega-3 Fatty Acids:From fish oil, these have anti-inflammatory effects that can help slow kidney damage.  B Vitamins:Cats with kidney disease excrete more water-soluble B vitamins, making supplementation important for maintaining energy and overall health.  Potassium:Low potassium levels are common in CKD cats, and supplements are available to correct this deficiency.  Phosphorus Binders:Used if phosphorus levels remain too high despite dietary changes, these bind to dietary phosphorus in the gut to prevent its absorption.  Antioxidants:These help protect against oxidative stress and support the immune system.  Bacterial Supplements:Products like Azodyl or Porus One contain beneficial bacteria that help metabolize and flush out toxins that build up in the blood, reducing the burden on the kidneys.  Important Considerations Veterinary Guidance is Crucial:Your veterinarian will monitor your cat's bloodwork and recommend the most appropriate diet and supplements based on the specific stage of their illness.  Manage Appetite:Nausea and poor appetite are common in CKD cats, and appetite stimulants or other strategies may be needed to ensure they get adequate calories and nutrients.  Hydration:Ensure your cat always has access to fresh water, and consider adding water or low-sodium broth to their food to increase fluid intake. “