고양이 신장 수치(BUN·크레아티닌·SDMA) 해석 가이드 — 정상 범위와 단계별 의미

Guide to Interpreting Cat Kidney Values (BUN, Creatinine, SDMA) — Normal Ranges and Stage Meanings

KidneyQ&AMeongsiljang Veterinary Advisory Board

To accurately interpret a cat’s kidney values, you need to look at BUN, creatinine, and SDMA together. Here’s a summary of each marker’s normal range, what different stages mean, and key points every pet owner should know.

What Are Cat Kidney Values?

A veterinarian reviewing a cat’s blood test results.

Feline kidney values refer to the BUN, creatinine, and SDMA levels assessed during blood tests to evaluate renal function. The key point is that no single value should be interpreted in isolation. SDMA is reported to rise earlier than creatinine, aiding in the detection of early changes. However, SDMA is not specific to kidney disease alone and can also increase in conditions such as dehydration, growth phases, or infections. Creatinine is less affected by diet but may appear low in cats with low muscle mass, while BUN is significantly influenced by diet, dehydration, and gastrointestinal bleeding. Therefore, these three values must be interpreted together and monitored over time for accurate assessment.

What BUN, Creatinine, and SDMA Mean

BUN (Blood Urea Nitrogen): This is a waste product produced when protein breaks down. Levels rise when the kidneys fail to filter it out properly. However, BUN can also increase due to high-protein diets, dehydration, or gastrointestinal bleeding.

Creatinine: This is a waste product generated by muscle metabolism. Because it is less affected by diet, it has long been the standard marker for assessing kidney function. Note that older cats with reduced muscle mass may show lower levels.

SDMA: This marker is reported to rise earlier than creatinine. It is less influenced by muscle mass, making it particularly useful for older cats. However, it is not specific to kidney disease alone; levels can also increase due to dehydration, growth phases, infections, or tumors. Therefore, SDMA should not be interpreted in isolation but rather alongside other values and diagnostic tests.

Normal Ranges for Cat Kidney Values (Reference Values)

Item	BUN	Creatinine	SDMA
Normal range	16–36 mg/dL	0.8–2.4 mg/dL	0–14 µg/dL
Borderline (recheck recommended)	36–50 mg/dL	1.6–2.8 mg/dL	14–18 µg/dL
Suspicious/abnormal	Over 50 mg/dL	Over 2.8 mg/dL	Over 18 µg/dL

Reference values may differ depending on the laboratory and equipment, so always check the reference range on the result sheet as well.

Meaning of Kidney Values by IRIS Stage

The International Renal Interest Society (IRIS) classifies chronic kidney disease into four stages based on creatinine and SDMA levels measured repeatedly while the patient is stable and well-hydrated.

Stage 1: Creatinine <1.6 (non-azotemic), SDMA <18 — Diagnosed by other renal abnormalities such as decreased urine concentrating ability, with almost no external clinical signs.

Stage 2: Creatinine 1.6–2.8, SDMA 18–25 — Increased water intake and urine output begin to appear.

Stage 3: Creatinine 2.9–5.0, SDMA 26–38 — Decreased appetite and weight loss become evident.

Stage 4: Creatinine >5.0, SDMA >38 — Increased risk of systemic symptoms and uremic crisis.

Because dehydration can cause these values to appear higher than they truly are, assessment should only be made after adequate rehydration.

Stages of Feline Kidney Disease Progression Diagram

When to Go to the Vet Immediately

A single elevated kidney value doesn’t automatically mean chronic kidney disease. However, if any of the following signs appear alongside it, prompt retesting and treatment are necessary: • Loss of appetite for more than 24 hours combined with repeated vomiting • An ammonia-like odor from the mouth (a sign of uremia) • Sudden weight loss and dehydration • Urine output that is more than double the usual amount, or conversely, barely any urine at all

When Values Are Borderline — Interpreting Them in Isolation Is Risky

If only BUN is elevated while creatinine and SDMA remain within normal ranges, dehydration, a high-protein diet, or gastrointestinal bleeding should be considered before kidney disease. Conversely, if only SDMA is slightly elevated with other values normal, it may indicate early-stage IRIS Stage 1 kidney disease, and retesting in 2–4 weeks is recommended. What truly matters is not a single value, but the trend of the values. Monitoring at the same laboratory every 2–3 months clearly reveals changes over time.

Monitoring a cat's kidney function through blood tests

Items to Check Alongside Kidney Values

Blood test results alone cannot provide a 100% accurate assessment of kidney function. Additional tests are necessary for a precise evaluation. Urine Specific Gravity (USG): If the kidneys fail to adequately concentrate urine or if isosthenuria is present, it suggests impaired renal concentrating ability. In early-stage kidney disease, a gradual decline in USG serves as an important clue. Urine Protein-to-Creatinine Ratio (UPC): This test confirms the presence of proteinuria, which is a criterion for IRIS substaging. Blood Pressure: Chronic kidney disease is a common underlying cause of hypertension, so blood pressure measurement and monitoring are essential. Blood pressure is also used as a criterion for IRIS substaging. Phosphorus and Potassium: Phosphorus levels may rise alongside azotemia, and potassium should be evaluated periodically. Abnormalities in these electrolytes are frequently observed in advanced stages of the disease.

Annual Kidney Value Testing Recommended for Senior Cats

Chronic kidney disease becomes increasingly common as pets age. The International Renal Interest Society (IRIS) considers 7 to 8 years and older as the high-risk age group requiring screening tests. Studies show that if detected in stages 1 or 2, when external symptoms are minimal, dietary management and other interventions can slow disease progression and improve both survival rates and quality of life. Therefore, regular monitoring of kidney values and urine tests is recommended starting at age 7, with more frequent check-ups as pets grow older.

What Owners Can Do When Values Are High

Don’t panic—follow these steps instead.

Ensure adequate hydration: Place fresh water in multiple locations and increase the proportion of canned food to reduce the burden on the kidneys.

Low-phosphorus diet: Renal prescription diets lower phosphorus content to slow disease progression. These should only be started under veterinary guidance.

Minimize stress: Environmental changes and conflicts with other cats can raise blood pressure and increase kidney strain.

Regular follow-up testing: Rechecking every 2–4 weeks is essential to monitor changes and track progress.

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

My dog’s BUN is slightly elevated, but creatinine and SDMA are normal. Is that okay?

BUN levels can also rise due to dehydration, a high-protein diet, or gastrointestinal bleeding, so it’s likely that kidney disease isn’t the cause. However, it’s safest to monitor the trend with a follow-up test in 2 to 4 weeks.

Is an SDMA level of 15 µg/dL indicative of kidney disease?

An SDMA level of 14–18 μg/dL falls within the borderline range. A single test isn't enough to make a definitive diagnosis, so we recommend retesting at the same laboratory in 2–4 weeks, along with checking urine specific gravity and urine protein.

My senior cat has a creatinine level of 2.0. Is that stage 1 or stage 2?

Creatinine alone isn’t enough to determine the stage. The IRIS stage is determined by combining SDMA, urine specific gravity, urine protein-to-creatinine ratio, and blood pressure. You should work with your veterinarian to interpret the results comprehensively.

Once the levels rise, can they go back down?

With acute kidney injury, your pet can often recover to normal levels with adequate fluid therapy and removal of the underlying cause. However, if a diagnosis of chronic kidney disease is made, a complete cure is unlikely, so the focus shifts to management strategies aimed at slowing the progression of the disease.

Can I have just the kidney values checked during a health screening?

It’s possible, but BUN, creatinine, and SDMA are typically included in a standard blood chemistry panel. To get an accurate assessment, you’ll also need urine specific gravity and a urine protein-to-creatinine ratio, so it’s best to request a dedicated kidney panel.

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References

[1] Langston CE, Eatroff AE. Chronic Kidney Disease. Small Animal Critical Care Medicine, 3rd Edition

[2] Little SE. The Cat: Clinical Medicine and Management, 2nd Edition — Urinary Tract Disease, Chronic Kidney Disease in Cats

[3] International Renal Interest Society (IRIS). IRIS Staging of CKD Guidelines

[4] Englar RE. The Veterinary Workbook of Small Animal Clinical Cases — Case 28: Feline CKD