Some experts believe Chronic Renal Disease (CRD) affects 8% or more of cats 10 years of age and older. It's a frustrating, potentially life-threatening kidney dysfunction we see most often in middle-aged and senior cats. Today, however, we have far better management techniques than the “Dark Ages” of feline CRD treatment.

What is CRD?

Chronic Renal Disease is the progressive loss of normal kidney function. It may arise from congenital abnormalities, urinary tract obstruction, trauma, infection, poisoning, diabetes, or other damage. In many older cats, the exact cause is never identified — it's often considered an age-related change, though many cats live long lives without ever developing CRD.

Whatever the cause, treating the underlying condition is the first step. After that, management of residual function becomes key.

Warning signs

CRD declines gradually, and even conscientious owners may miss early signs. Watch for:

Unexplained weight loss
Dull, unkempt coat
Lethargy
Decreased appetite
Increased thirst
Vomiting food or small amounts of yellowish fluid

Any of these warrant an urgent vet visit. Blood and urine tests can confirm the diagnosis and start treatment.

The protein-restriction myth

Traditional veterinary medicine prescribes protein-restricted diets for cats with CRD. This is misguided and can cause more harm than good. The recommendation was originally developed in the 1940s for dogs, which are omnivores. Cats are obligate carnivores with naturally high protein requirements — and a sick cat may need more protein than a healthy one, not less.

Low-protein prescription “kidney diets” are unpalatable to cats. When the CRD cat refuses to eat the only food offered, the owner becomes frustrated and the cat declines. The starving cat wastes away, and CRD gets all the blame.

There have never been scientific studies showing long-term benefits from reducing high-quality protein in cats with CRD.

What actually helps: phosphorus, not protein

What benefit there is in protein-restricted diets comes from their phosphorus restriction. In cats with insufficient kidney function, high dietary phosphorus can accelerate further decline. But limiting phosphorus by limiting protein is “throwing the baby out with the bathwater.”

Better approaches:

Phosphate binders added to regular palatable, high-protein wet food remove substantial dietary phosphorus.
Chopped, cooked egg white mixed into wet food — high in top-quality protein, no phosphate. It effectively dilutes phosphorus in the diet.

No dry food

Dry kibble is inappropriate for any cat, but especially dangerous for the CRD patient. The cat's kidney is a remarkable water-saving organ, but CRD impairs that ability. A cat on dry food is chronically dehydrated — and in CRD, that can be life-threatening. Years of dry-food consumption may even contribute to developing CRD in the first place.

Modern CRD management

Early diagnosis is critical. Any weight loss, lethargy, repeated vomiting, or increased thirst warrants a vet visit.
Avoid protein-restricted diets. Feed high-quality, high-protein wet food. Protein does not “burn out” the kidneys.
Control phosphorus with binders or egg white instead of starving the cat of protein. If phosphorus is normal, your vet may start calcitriol supplementation.
Measure blood pressure. Many CRD cats develop hypertension. ACE inhibitors like benazepril are extremely valuable — benefits go beyond blood pressure control. If benazepril alone isn't enough, amlodipine may be added.
Treat urinary tract infections with appropriate antibiotics.
Subcutaneous fluids at home are often better than IV. Easier to administer, less risk of overhydration, and lifesaving when given regularly. Supplement with potassium and B-vitamins to replace what increased fluid flow removes.
Address anemia. Failing kidneys produce less erythropoietin; injections of this hormone (or a blood transfusion in severe cases) help.
Recheck regularly. Successful CRD management is an ongoing team effort.

Calcitriol and renal hyperparathyroidism

Cats with CRD typically develop renal secondary hyperparathyroidism. As kidneys fail, they lose the ability to activate vitamin D and excrete phosphorus, causing a cascade that pulls calcium from bones and deposits calcium-phosphate crystals in soft tissues. Daily low-dose calcitriol (the active form of vitamin D) can stop or greatly slow this cycle in mild-to-moderate CRD. Used properly with monitoring, it's one of the most promising new tools we have.

A note on BUN

Cats on naturally high-protein diets have slightly higher BUN levels than “normal” ranges (which were established on cats fed lower-protein commercial foods). Urea is non-toxic — a mild elevation in a CRD cat on a high-protein diet is not harmful. Drugs marketed to lower BUN (such as Azodyl) treat a diagnostic marker, not the disease, and may complicate monitoring without improving function.

The takeaway

Modern CRD management — high-quality wet food, phosphorus control, ACE inhibitors, subcutaneous fluids at home, and selective use of calcitriol — can give your cat years of good-quality life. Talk with a veterinarian familiar with these modern protocols.

Kidney Disease in Cats: A Modern Approach to an Old Enemy