고양이 신장 기능 혈액검사(BUN·Cr·SDMA) 증상과 원인, 진단·치료와 관리 포인트 총정리

A Complete Guide to Cat Kidney Blood Tests (BUN, Cr, SDMA) — From Interpreting Values to Management

KidneyDiseasesMeongsiljang Veterinary Advisory Board

Blood tests for kidney function (BUN, Cr, SDMA) are essential for the early detection of chronic kidney disease in cats. These tests allow for an accurate assessment of whether kidney function has declined.

What Are Cat Kidney Function Blood Tests (BUN, Cr, SDMA)?

A scene of a veterinarian preparing a cat for a blood test, with samples labeled SDMA, BUN, and Cr.

Blood tests for kidney function in cats (BUN, Cr, SDMA) are essential for evaluating the kidneys’ filtering capacity. BUN (Blood Urea Nitrogen) reflects the kidneys’ ability to eliminate waste products; elevated levels suggest possible kidney dysfunction. However, BUN can also be influenced by non-renal factors such as diet (high protein intake) and muscle mass. Creatinine (Cr) is a metabolic byproduct produced by muscles, and its blood concentration rises when the kidneys fail to filter it properly. SDMA (symmetric dimethylarginine) is a substance generated at a steady rate from the breakdown of intracellular proteins and primarily excreted by the kidneys, correlating well with glomerular filtration rate (GFR). It can rise above reference ranges earlier than creatinine, making it a sensitive marker for detecting early kidney damage. Analyzing these three indicators together helps determine whether kidney function is declining, and early detection is crucial for timely treatment.

Main Causes of Declining Kidney Function

Kidney function decline in cats can stem from various causes. - Aging: A common underlying factor for chronic kidney disease in older cats, where kidney function gradually deteriorates over time. - Infections and inflammation: Kidney infections or inflammation, such as pyelonephritis, can cause long-term damage to the kidneys. - Exposure to toxic substances: Ingestion of lily leaves, flowers, or pollen (Lilium and Hemerocallis species), or ethylene glycol (antifreeze), can cause acute kidney injury in cats. Cats are particularly vulnerable to ethylene glycol. - Urinary tract obstruction: Urethral obstruction is the most common cause of acute kidney injury in cats. When urine flow is blocked, it quickly places stress on the kidneys. - Dehydration and heart failure: Reduced blood flow to the kidneys due to fluid deficiency or heart issues (prerenal causes) can lead to temporary functional decline. Identifying the underlying cause is the first step toward treatment.

An anatomical diagram illustrating reduced kidney filtration function

Key Symptoms and Signs

The most common signs of declining kidney function in cats are increased thirst and more frequent urination. You may also notice weight loss, a reduced appetite, vomiting, and lethargy. These symptoms occur because the kidneys can no longer effectively filter waste products from the body, causing them to build up.

Excessive thirst: Your cat drinks water more often and empties its water bowl frequently.

Frequent urination: Your cat urinates multiple times a day and may spend longer than usual in the litter box.

Weight loss: Muscle mass decreases, making bones more prominent.

Loss of appetite: Your cat may refuse treats or regular food, or vomit shortly after eating.

Recurring vomiting: This often happens in the morning.

Lethargy: Your cat remains inactive, sitting or lying in the same spot all day.

A scene of a cat drinking water and near the litter box

Signs Requiring Immediate Veterinary Visit

If your cat hasn’t drunk water for 24 hours or hasn’t urinated at all, you should take them to the vet immediately. This could be a sign of acute kidney injury, and early treatment is crucial for survival.

Diagnostic Methods and Testing Procedures

Diagnosing kidney function in cats involves both blood and urine tests. - Blood tests: Measure BUN, creatinine, and SDMA levels to assess kidney filtration function. SDMA is particularly useful for early detection, as it can identify even early-stage kidney damage. - Urine tests: Check urine concentration (specific gravity) and the presence of protein to evaluate the kidneys' ability to concentrate urine and detect any damage. The veterinarian will interpret all these results together to determine the stage of kidney function and decide on the treatment plan. Regular check-ups are essential for early detection and prevention.

A veterinarian analyzing a cat's blood test results.

Treatment Methods and Step-by-Step Management

Treatment for decreased kidney function varies depending on the underlying cause. The main approaches include fluid therapy, prescription diets, and medication. With early diagnosis, your veterinarian will create a customized treatment plan based on your pet’s weight and overall condition. Since treatment may be lifelong, regular check-ups and ongoing management are essential.

Fluid Therapy: Subcutaneous injections or oral fluids are administered to prevent dehydration.

Prescription Diet: Specialized food helps reduce kidney strain by controlling protein and phosphorus levels.

Medication: Drugs are prescribed to manage complications such as high blood pressure, anemia, and gastrointestinal issues.

Blood Test Monitoring: Regular blood tests every 1–3 months help track your pet’s condition.

A scene of a cat receiving subcutaneous fluid therapy.

Daily Care Points at Home

Maintaining your cat’s kidney health requires consistent, ongoing care. It’s important to refresh their water frequently and place multiple water bowls around the home. Consistently feeding a prescribed renal diet and monitoring their condition through regular veterinary check-ups are also essential. Additionally, keeping a quiet environment and maintaining a stable daily routine helps minimize stress, which is crucial for their well-being.

Refresh water frequently: Change the water at least two to three times a day.

Place water bowls in various locations: Distribute water bowls throughout your home.

Consistently feed prescribed renal diet: Provide the veterinarian-recommended food consistently.

Schedule regular check-ups: Monitor kidney function with blood tests every six to twelve months.

Minimize stress: Avoid disrupting your cat’s established habits and maintain a calm, quiet environment.

A scene with multiple water bowls inside the house, showing a cat drinking.

Breed-Specific Precautions and Prevention of Recurrence

Chronic kidney disease in cats becomes increasingly dangerous with age, making early and regular kidney function tests especially important for senior cats. SDMA levels can rise earlier than creatinine, aiding in early detection, so it’s a good idea to consult your veterinarian to establish a routine screening plan. To slow disease progression, consistent dietary management with controlled phosphorus and protein intake, along with adequate hydration, is essential. Regular check-ups are also necessary to monitor and manage your cat’s condition over time.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Why is kidney function testing important for cats?

The kidneys are vital organs responsible for filtering waste from the body. Early testing can detect declining kidney function, allowing you to start management promptly without missing the optimal treatment window. This helps slow disease progression and maintain your pet’s quality of life.

What is the difference between BUN and SDMA?

While BUN levels can be influenced by various non-renal factors such as diet and muscle mass, SDMA correlates well with glomerular filtration rate (GFR) and rises earlier than creatinine, making it advantageous for detecting early kidney damage.

If my cat has kidney disease, how should I change its diet?

It's best to switch to a special diet recommended by your veterinarian. This type of food helps reduce the burden on the kidneys by controlling the levels of protein and phosphorus.

What should I do if my cat with kidney disease isn’t drinking enough water?

Place water bowls in multiple locations, refresh the water frequently, and consider using a flowing automatic water fountain. This ensures your pet always has access to fresh water, and if needed, your veterinarian can administer subcutaneous fluids.

What is the prognosis (life expectancy) for cats with kidney disease?

With early diagnosis and proper dietary and hydration management, the progression of the condition can be slowed, allowing your pet to maintain a good quality of life and remain relatively stable. However, prognosis varies depending on the individual and the stage of disease, so regular check-ups to monitor their condition are essential.

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References

[1] Langston, C.E. et al. (2023) Small Animal Critical Care Medicine, 3rd Edition. Elsevier.

[2] The Cat, Clinical Medicine and Management, 2nd Edition (2022). Elsevier.

[3] Veterinary Workbook of Small Animal Clinical Cases (2021). Wiley-Blackwell.