Chronic kidney disease: stages and home care

The diagnosis lands in the exam room the way a lot of bad diagnoses land. The owner has noticed something subtle — the cat is drinking more, the dog is losing weight, the appetite is "off" — and the bloodwork comes back with a creatinine of 3.2 mg/dL, a BUN of 45, a SDMA of 25, and a urine specific gravity of 1.018. The owner is in the chair, and I am on the other side, and the conversation that follows is one of the most important conversations in small-animal medicine. The diagnosis is chronic kidney disease (CKD), and the disease is not curable. The disease is, however, manageable. With the right staging, the right home-care protocol, the right diet, the right medications, and the right monitoring schedule, the dog or cat with CKD can live for months to years longer than the dog or cat whose CKD is diagnosed and then ignored. The difference is owner engagement. The protocol, when followed, works.

This article is going to walk you through what CKD actually is, the IRIS staging system that has become the international standard for assessing severity, the home-care protocol at each stage, the diet and medication interventions that meaningfully extend survival, and the honest prognosis at each stage. I am going to be direct about the prognosis, because the owner who is making decisions about a CKD pet needs accurate information about what to expect, not vague reassurance.

The framework that follows is, with appropriate modifications, applicable to both dogs and cats. The two species have somewhat different trajectories and somewhat different therapeutic options, and I will call out the species-specific differences where they matter.

What chronic kidney disease actually is

Chronic kidney disease is the progressive, irreversible loss of functional kidney tissue. The kidneys are paired organs responsible for filtering waste products from the blood, regulating fluid and electrolyte balance, producing hormones (erythropoietin for red blood cell production, calcitriol for calcium regulation, renin for blood pressure regulation), and concentrating urine. The functional unit of the kidney is the nephron, and the dog is born with roughly 400,000–900,000 nephrons per kidney, the cat with roughly 200,000–500,000 per kidney. CKD is the condition in which a sufficient number of nephrons are lost that the remaining nephrons cannot adequately perform these functions, and the result is the accumulation of nitrogenous waste products in the blood (azotemia), the loss of urine-concentrating ability, the disruption of electrolyte and acid-base balance, and the secondary effects of those changes on the rest of the body.

The key word is "irreversible." Once a nephron is lost to CKD, it does not regenerate. The remaining nephrons can compensate (the kidney has significant functional reserve, which is why CKD is often advanced before the clinical signs appear), but the loss is permanent. The disease is progressive, meaning the loss continues over time, but the rate of progression is variable and is influenced by the underlying cause, the medical management, and the dietary management. The slow-progressing CKD, well-managed, can produce years of good-quality life. The fast-progressing CKD, poorly managed, can produce uremic crisis and death within months.

The causes of CKD in dogs and cats include:

• Idiopathic (most common in cats). The cause is not identified, but the disease is presumed to involve chronic tubulointerstitial inflammation, fibrosis, and a gradual loss of nephrons. This pattern is the most common form of CKD in older cats and accounts for a large fraction of the CKD cases I see in practice.

• Congenital (polycystic kidney disease in Persians and other breeds, renal dysplasia in some breeds). A developmental abnormality that produces CKD, often in middle age. Persian, Exotic Shorthair, and British Shorthair cats are at elevated risk. In dogs, the breed predispositions include the Bull Terrier, the Cairn Terrier, the German Shepherd, the Lhasa Apso, the Shar-Pei, and the Soft-Coated Wheaten Terrier.

• Acquired. Chronic pyelonephritis (kidney infection), chronic glomerulonephritis (immune-mediated), nephrotoxicity (NSAIDs, aminoglycosides, lily exposure in cats, grape/raisin exposure in dogs, ethylene glycol antifreeze), chronic urinary obstruction, kidney stones, and a long list of less common conditions.

The most common form in dogs is acquired (often a combination of chronic glomerular disease and age-related nephron loss). The most common form in cats is idiopathic. The clinical picture at presentation is similar in both species, but the prognostic trajectory is somewhat different — cats tend to have a slower, more variable progression than dogs.

The IRIS staging system

The International Renal Interest Society (IRIS) has developed a staging system that has become the international standard for assessing CKD severity in dogs and cats. The system is built on two main axes — the serum creatinine (or, increasingly, the SDMA, a more sensitive marker of kidney function) and the presence or absence of clinical signs — and it produces a four-stage classification that is used to guide treatment decisions and to communicate prognosis.

IRIS Stage 1. Serum creatinine is within the laboratory's normal reference range (typically <1.4 mg/dL in dogs, <1.6 mg/dL in cats), but the SDMA is elevated (>14 µg/dL in dogs, >18 µg/dL in cats) or other markers of kidney damage are present (proteinuria, abnormal imaging). The pet is typically asymptomatic. The diagnosis is often incidental — found on a screening bloodwork in a senior pet, or found on a workup for a different problem.

IRIS Stage 2. Serum creatinine is mildly elevated (1.4–2.0 mg/dL in dogs, 1.6–2.8 mg/dL in cats). The pet is typically asymptomatic or mildly symptomatic (slightly increased thirst, slightly increased urination, mild weight loss). The disease is detectable on routine bloodwork.

IRIS Stage 3. Serum creatinine is moderately elevated (2.1–5.0 mg/dL in dogs, 2.9–5.0 mg/dL in cats). The pet is typically symptomatic — increased thirst and urination, weight loss, decreased appetite, intermittent vomiting, mild to moderate lethargy. The disease is significant and the intervention is active.

IRIS Stage 4. Serum creatinine is severely elevated (>5.0 mg/dL in both species). The pet is significantly symptomatic — severe lethargy, severe appetite loss, vomiting, possible uremic crisis, possible neurological signs (uremic encephalopathy). The disease is advanced and the prognosis is guarded.

Within each stage, the IRIS system further sub-classifies based on proteinuria (the urine protein-to-creatinine ratio) and on blood pressure. The proteinuria sub-class is important because significant proteinuria is a negative prognostic factor and is a specific treatment target. The blood pressure sub-class is important because systemic hypertension is both a common complication of CKD and a driver of further kidney damage.

The staging is not a one-time assessment. The staging is repeated at every recheck, because the stage can progress (which is the typical trajectory) or, with good management, can remain stable for extended periods. The rate of progression is the key prognostic variable, and the rate is what the management is trying to slow.

The home-care protocol by stage

The home-care protocol varies significantly by stage, because the clinical needs of the pet vary significantly by stage. The protocol I describe below is the protocol I use in my own practice, and it is grounded in the published evidence and the IRIS treatment guidelines.

IRIS Stage 1: The detection phase. The pet is typically asymptomatic, the diagnosis is often incidental, and the home-care protocol is mostly about confirming the diagnosis, ruling out reversible causes, and establishing the baseline.

• Diagnostic workup. A complete blood count, full chemistry, urinalysis with culture (to rule out subclinical infection), urine protein-to-creatinine ratio, blood pressure measurement, and imaging (abdominal ultrasound) to assess kidney size, shape, and architecture. The workup is to rule out reversible causes (early pyelonephritis, partial obstruction, drug-induced nephrotoxicity) and to establish the baseline.

• Diet. Most Stage 1 pets are not yet on a prescription renal diet, but the transition to a maintenance diet that is lower in phosphorus and higher in omega-3 fatty acids is reasonable. Some veterinarians recommend transitioning to a prescription renal diet at Stage 1; others wait until Stage 2.

• Monitoring. Recheck bloodwork, urinalysis, and blood pressure every 6 months. The pet is monitored, not yet treated aggressively.

• Home care. Fresh water at all times. Monitor water intake and urine output (without becoming obsessive). Report any changes to the vet.

IRIS Stage 2: The early-intervention phase. The pet is mildly symptomatic or asymptomatic, the diagnosis is established, and the home-care protocol is actively engaged.

• Prescription renal diet. The most important intervention at this stage. A prescription renal diet (Hill's k/d, Royal Canin Renal, Purina NF) is, in the published studies, the single most effective intervention for slowing CKD progression. The diet is restricted in phosphorus, restricted in protein (in dogs; in cats, the protein is restricted in high-quality form rather than in total amount), elevated in omega-3 fatty acids, and supplemented with B vitamins and antioxidants. The published evidence is consistent that early dietary intervention (Stage 2 or even late Stage 1) is significantly more effective than late dietary intervention (Stage 3 or 4).

• Phosphate binders. If the diet alone is not enough to keep the serum phosphorus in the target range (typically <4.5 mg/dL in dogs, <5.0 mg/dL in cats at Stage 2), a phosphate binder (calcium carbonate, lanthanum carbonate, sevelamer) is added to the food. The binder prevents the dietary phosphorus from being absorbed, and the effect is to drop the serum phosphorus without requiring a further reduction in dietary protein.

• Omega-3 fatty acid supplementation. EPA and DHA, 50–75 mg per kg per day of combined EPA+DHA, with the marine oil specifically (not flax). The anti-inflammatory and renoprotective effects are well-documented.

• Blood pressure management. If the pet is hypertensive (systolic >160 mmHg in cats, >180 mmHg in dogs), an antihypertensive medication (amlodipine, a calcium channel blocker, is the first-line choice in cats; ACE inhibitors are sometimes used in dogs) is started. The blood pressure should be measured at every recheck.

• Monitoring. Recheck every 3–6 months, with bloodwork, urinalysis, urine protein-to-creatinine ratio, and blood pressure. The trend is what matters.

• Home care. Fresh water at all times. Monitor water intake, appetite, body weight, and behavior. Report any changes to the vet.

IRIS Stage 3: The active-management phase. The pet is symptomatic, the disease is significant, and the home-care protocol is intensive.

• Prescription renal diet, continued. The diet is essential, and compliance becomes more challenging because the pet's appetite is reduced. Warming the food, offering multiple small meals, mixing wet and dry formulations, and (in some cases) using appetite stimulants (mirtazapine, capromorelin) are part of the protocol. The owner who is struggling with food intake should talk to the vet about the options, because the diet matters.

• Phosphate binders, continued. The dose may need to be increased as the disease progresses.

• Anti-nausea medication. Maropitant (Cerenia) is the first-line anti-nausea medication for CKD pets. The dose is 1 mg/kg orally or 2 mg/kg subcutaneously, every 24 hours. Ondansetron is an alternative. Mirtazapine is a useful adjunct that combines anti-nausea with appetite stimulation (the transdermal formulation, applied to the inner ear, is well-tolerated by most cats).

• Subcutaneous fluid therapy. The kidney's ability to concentrate urine is failing, and the pet is losing water through dilute urine. Subcutaneous fluid administration (typically 100–200 mL of lactated Ringer's solution, given under the skin, every 24–48 hours, depending on the pet's needs) is the home-care intervention that often produces the most visible improvement in the pet's quality of life. The pet becomes more active, more engaged, and more interactive within 24–48 hours of starting fluids. The technique is simple, the equipment is provided by the vet, and most owners learn to administer the fluids within 1–2 sessions.

• ACE inhibitor (in proteinuric cases). If the pet has significant proteinuria (urine protein-to-creatinine ratio >0.5 in dogs, >0.4 in cats), an ACE inhibitor (benazepril, enalapril) is started. The drug reduces the intraglomerular pressure and slows the progression of proteinuric kidney disease.

• Erythropoietin supplementation (if anemic). The kidney produces erythropoietin, and a CKD pet may become anemic as the disease progresses. The anemia contributes to the lethargy, the reduced appetite, and the overall decline. Darbepoetin or recombinant erythropoietin, given by subcutaneous injection, is the treatment. The response takes 2–4 weeks.

• Monitoring. Recheck every 2–3 months, with the same panel as Stage 2.

• Home care. Same as Stage 2, with the addition of subcutaneous fluid administration. The owner should learn the technique, the dosing, and the recognition of fluid overload (a rare but real complication, especially in pets with concurrent heart disease).

IRIS Stage 4: The palliative phase. The pet is significantly symptomatic, the disease is advanced, and the home-care protocol is focused on quality of life.

• All of the above, intensified. The diet, the binders, the anti-nausea medications, the subcutaneous fluids, the antihypertensives — all continued and possibly increased.

• Hospice focus. The Stage 4 CKD pet is a hospice pet. The owner and the vet are working together to maintain the pet's quality of life for as long as it is meaningful, and to recognize when the quality of life has declined to a point where euthanasia is the kindest choice.

• Monitoring. Recheck every 4–8 weeks, or as needed. The frequency is driven by the pet's clinical picture.

• Home care. Same as Stage 3, with a focus on the pet's comfort, the pet's appetite (even if reduced), the pet's interaction with the family, and the pet's good days and bad days.

The diet, in detail

The prescription renal diet is the single most important intervention for the CKD pet, and the evidence base is among the strongest in veterinary internal medicine. The 2016 EPIC trial (Evaluating Prevention of progression in Chronic kidney disease) showed that early dietary intervention in cats with IRIS Stage 2–3 CKD reduced the risk of uremic crisis by 24% and extended the median survival. The earlier the diet is started, the larger the effect.

The macronutrient profile of a prescription renal diet:

• Phosphorus restricted. Typically 0.3–0.6% on a dry-matter basis, compared to 0.7–1.0% in a maintenance diet. The phosphorus restriction reduces the risk of renal secondary hyperparathyroidism, which is a major driver of CKD progression.

• Protein restricted (in dogs), restricted in high-quality form (in cats). The protein restriction reduces the nitrogenous waste load on the kidneys. In cats, the protein restriction is more moderate than in dogs, because the cat is an obligate carnivore and severe protein restriction produces muscle wasting. The published evidence on protein restriction in cats is more nuanced than in dogs.

• Omega-3 fatty acids elevated. EPA and DHA at 0.5–1.0% of dry matter, for anti-inflammatory and renoprotective effects.

• Sodium mildly restricted. To support blood pressure management.

• B vitamins elevated. To compensate for urinary losses.

• Potassium elevated (in cats). To compensate for renal potassium wasting.

The leading prescription renal diets, in order of my preference:

• Hill's Prescription Diet k/d (canned and dry). The most-cited prescription renal diet in the published literature. Strong palatability, well-balanced nutrient profile, good clinical results.

• Royal Canin Veterinary Diet Renal Support (canned and dry). A range of formulations (Early, Moderate, Advanced) that are matched to the stage of the disease. Good palatability, well-balanced profile.

• Purina Pro Plan Veterinary Diets NF (canned and dry). Another well-validated option, with a strong track record.

For pets that refuse the prescription diet, a home-cooked diet formulated by a board-certified veterinary nutritionist (DACVN) is a real alternative. The DACVN will design a recipe that hits the macronutrient targets, the micronutrient targets, and the caloric targets appropriate for the pet's stage and body condition.

The medications, in detail

The medication protocol is staged, with the medications added as the disease progresses. The complete medication list for a Stage 3–4 CKD pet is:

• Phosphate binder (calcium carbonate, lanthanum carbonate, sevelamer, or a combination), with each meal.

• Antihypertensive (amlodipine, benazepril, telmisartan, or a combination) if the pet is hypertensive.

• Anti-nausea (maropitant, ondansetron, mirtazapine) if the pet is nauseated.

• Appetite stimulant (mirtazapine, capromorelin) if the pet's appetite is reduced.

• ACE inhibitor or ARB (benazepril, enalapril, telmisartan) if the pet is proteinuric.

• Erythropoietin (darbepoetin, recombinant EPO) if the pet is anemic.

• Calcitriol (active vitamin D) if the pet has renal secondary hyperparathyroidism.

• Potassium supplementation (potassium gluconate) if the pet is hypokalemic.

• B-vitamin supplementation to compensate for urinary losses.

• H2 blocker or proton pump inhibitor (famotidine, omeprazole) if the pet has GI ulceration secondary to uremia.

The owner who is at the vet clinic with a newly diagnosed Stage 3 CKD pet will leave with a long list of medications. The list is intimidating, but the medications are doing different jobs, and the combination is what produces the visible improvement. The owner who engages with the protocol is the owner whose pet stabilizes and lives for months to years. The owner who tries to do the minimum is the owner whose pet declines.

The honest prognosis, by stage

The prognosis is the question that every owner asks, and it is the question that every vet dreads, because the answer is "it depends" and the owner wants a number. The honest answer, with the data I have, is:

• IRIS Stage 1: many pets at Stage 1 do not progress to Stage 2 for years, and some never progress. The median survival is 3+ years from diagnosis. Many Stage 1 pets die of something else (cancer, heart disease) before they die of CKD.

• IRIS Stage 2: with appropriate dietary and medical management, the median survival is 2–3 years from diagnosis. Without management, the median survival is 1–2 years.

• IRIS Stage 3: with appropriate management, the median survival is 1–2 years from diagnosis. Without management, the median survival is 3–6 months.

• IRIS Stage 4: with appropriate management, the median survival is 1–6 months from diagnosis. Without management, the median survival is 2–4 weeks.

The numbers are real, but they are population averages, and the individual pet's trajectory is highly variable. The Stage 2 cat that is well-managed may live 5+ years. The Stage 2 cat that is poorly managed may progress to Stage 4 within 12 months. The variables that predict the trajectory include the underlying cause, the rate of progression at diagnosis, the proteinuria status, the blood pressure, the response to dietary intervention, and the owner's ability to comply with the medication and monitoring protocol.

The bottom line

Chronic kidney disease is a real, common, and significant condition in senior dogs and cats. The disease is not curable, but it is manageable. The IRIS staging system gives a framework for assessing severity and for guiding treatment. The home-care protocol varies by stage, but the core interventions — the prescription renal diet, the phosphate binder, the omega-3 supplementation, the subcutaneous fluids (in later stages), the antihypertensives (in hypertensive cases), the anti-nausea medications (in nauseated cases) — are evidence-based and effective.

The pet whose owner engages with the protocol, with the vet, with the recheck schedule, with the medication administration, and with the diet is the pet that has the best chance of a long, good-quality life. The pet whose owner is overwhelmed, disengaged, or skeptical of the protocol is the pet that has a shorter, more difficult trajectory. The difference is owner engagement. The protocol, when followed, works.

The diagnosis is not the end. The diagnosis is the start of a structured, evidence-based, supported management plan that extends the pet's life and maintains the pet's quality of life. The owner who is reading this article is the owner who is willing to engage. That is the most important variable. Everything else follows.

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About the author

James Morrison, DVM, is a small-animal internist with a focus on chronic disease management in senior dogs and cats. He has worked in general practice and specialty referral settings across the Mountain West, and writes regularly on the practical interface between evidence-based medicine and the day-to-day realities of managing a chronically ill pet at home.