How to Read Your Dog’s BUN and Creatinine Levels — Interpreting Kidney Test Results

KidneyQ&AMeongsiljang Veterinary Advisory Board

We’ve put together a guide to help you understand your dog’s BUN, creatinine, and SDMA blood test results, including how to interpret them yourself, normal reference ranges, and what each level means.

What Are Canine Kidney Values? — Key Points at a Glance

Canine kidney values refer to three key indicators of kidney function measured through blood tests: BUN (blood urea nitrogen), creatinine, and SDMA. The most important factor is not a single value but the trend over time. Rather than focusing on one result, observing changes in these values when the same tests are repeated at intervals of six months to a year provides a more accurate picture of kidney health. Even if the values remain within the normal range, a gradual upward trend could be an early sign of kidney disease.

What Do BUN, Creatinine, and SDMA Mean?

All three markers reflect the kidneys’ ability to filter waste, but they differ in sensitivity. - BUN (Blood Urea Nitrogen): A waste product of protein metabolism. It fluctuates significantly due to factors such as diet, dehydration, and gastrointestinal bleeding. - Creatinine: A waste product produced at a steady rate by muscles. It provides a more stable reflection of kidney function than BUN. - SDMA (Symmetric Dimethylarginine): An early indicator that rises when kidney function is impaired by approximately 40%. It detects changes much earlier than creatinine (which typically rises only after about 75% loss of function) and is more reliable because it is less affected by age, body size, and muscle mass.

Normal Reference Ranges for Canine Kidney Values

Item	Normal range	Caution stage	Notes
BUN	8–25 mg/dL	25–50 mg/dL	Greatly affected by diet and dehydration
Creatinine	0.3–1.3 mg/dL	1.4–2.8 mg/dL	Affected by muscle mass
SDMA	0–14 µg/dL	14–20 µg/dL	For early detection
Urine specific gravity (USG)	1.030 or higher	1.013–1.029	Meaningful only when viewed together

Reference values may differ by testing laboratory and instrument. Be sure to compare with the reference range column on your test report.

Immediate Veterinary Revisit Required for These Levels

If your pet’s creatinine has ever exceeded 2.8 mg/dL, BUN over 50 mg/dL, or SDMA over 25 µg/dL, further testing—such as urinalysis, blood pressure measurement, and abdominal ultrasound—is necessary. The situation becomes even more urgent if these results are accompanied by decreased appetite, vomiting, or increased thirst and urination. Even in pets that appear healthy, kidney function must decline by more than 75% before creatinine levels rise above the normal range, so never dismiss a single mildly elevated result as insignificant.

Slightly Elevated Levels — Is It a Genuine Kidney Issue?

BUN and creatinine levels can fluctuate due to factors unrelated to kidney function. To determine whether there is a genuine kidney issue, it is important to check the following before testing: - Fasting status: BUN levels may temporarily rise after consuming a protein-rich meal. It is recommended to fast for 12 hours before the test. - Hydration status: BUN levels can increase due to non-kidney-related causes (prerenal elevation) after exposure to hot weather, vomiting, or diarrhea. - Muscle mass: Large-breed dogs with more muscle mass may have slightly higher creatinine levels, while senior dogs or those with muscle loss may have lower levels. - Single result vs. trend: Do not rely on a single test result; instead, retesting every 2–4 weeks is recommended.

A veterinarian drawing blood from a puppy.

IRIS Staging — The 4 Stages of Kidney Disease

The International Renal Interest Society (IRIS) classifies chronic kidney disease into four stages based on creatinine levels. A higher stage indicates less remaining kidney function. Staging is determined by the average of at least two measurements taken while the patient is fasting and well-hydrated. A single test result should never be used to definitively assign a stage.

Creatinine Criteria by IRIS Stage (Dogs)

Item	Creatinine (mg/dL)	Clinical significance	Owner action
Stage 1	< 1.4	Kidney damage present but values normal	Confirm with SDMA and urinalysis, recheck every 6 months
Stage 2	1.4–2.8	Mild — no or subtle symptoms	Start dietary management, recheck every 3–6 months
Stage 3	2.9–5.0	Moderate — polydipsia/polyuria, decreased appetite	Start prescription diet, phosphorus restriction, medication
Stage 4	> 5.0	Severe — uremic symptoms	Hospitalization, fluids, intensive care needed

Stage determination is based on two or more measurements taken in a stable state. A single spike is not grounds for confirming a stage.

Why Is SDMA Testing Important?

SDMA levels begin to rise when kidney function is impaired by approximately 40%. In contrast, creatinine levels only exceed the normal range after more than 75% of kidney function is lost, which is why early-stage kidney disease was often missed before SDMA testing became available. Because SDMA is less affected by age, body size, and muscle mass, it serves as a more reliable early indicator than creatinine. - Senior dogs (7 years and older): We recommend including SDMA in annual wellness exams. - Trend monitoring: Even if SDMA levels remain within the normal range, a consistent year-over-year increase may signal early changes. - Breed considerations: Certain breeds are at higher genetic risk for kidney disease and may require earlier and more frequent monitoring. If you suspect kidney disease, please also review our Guide to Chronic Kidney Disease in Dogs.

An elderly dog resting comfortably at home

Values to Check Together — Do Not Interpret in Isolation

Relying solely on BUN and creatinine levels can be misleading. It’s essential to also check phosphorus (P), potassium (K), urine specific gravity (USG), and urine protein-to-creatinine ratio (UPC) on the same test panel. For instance, even if creatinine is slightly elevated, a USG above 1.030 indicates that the kidneys are still maintaining their concentrating ability. Conversely, if creatinine falls within the normal range but USG is below 1.020 and proteinuria is present, early kidney damage should be suspected.

Next Steps When Levels Are High

When abnormal kidney values appear, we take a step-by-step approach. - Recheck after 2–4 weeks in a fasting and calm state: To determine if the changes are temporary - Additional urine tests: Check urine specific gravity, proteinuria (UPC), and urinary sediment - Blood pressure measurement: Hypertension is commonly associated with chronic kidney disease, and both blood pressure and proteinuria are used as additional classification criteria in IRIS staging - Abdominal ultrasound: To assess kidney size, structure, and the presence of stones or tumors - Dietary adjustments: Consider introducing a prescription diet restricted in protein and phosphorus - Set recheck intervals: Monitor every 1–6 months depending on the stage Always consult your veterinarian before starting any prescription diet or supplements on your own.

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

Only the BUN is slightly elevated, while creatinine is normal. Could this be a kidney issue?

An isolated rise in BUN is more likely due to non-renal causes. Common triggers include recent high-protein meals, dehydration, gastrointestinal bleeding, or fever. We recommend retesting after 2–4 weeks while the pet is fasted for 12 hours. If BUN remains elevated or if creatinine and SDMA also increase, we then evaluate for kidney disease.

Do senior dogs with low muscle mass tend to have lower creatinine levels?

That’s correct. Since creatinine is produced in muscle tissue, senior dogs with significant muscle loss may still show normal creatinine levels even if their kidney function has declined. In such cases, evaluating SDMA, urine specific gravity, and proteinuria together provides a much more reliable assessment.

Does a normal test result mean I can be reassured for a full year?

For healthy dogs under seven years of age, annual testing is sufficient. However, we recommend testing every six months, including SDMA, for dogs aged seven and older or those belonging to breeds prone to kidney disease, such as Cocker Spaniels, Shetland Sheepdogs, Korean Jindo, and Bull Terriers. Monitoring trends over time is more important than relying on a single result.

Is there anything I should prepare before the test?

For accurate kidney function results, it’s best to fast your pet for 8–12 hours before the test. However, water can be offered freely as usual. Also, please bring a list of any medications, supplements, or dietary changes your pet has had in the past two weeks, as this will help ensure a more precise interpretation of the results.

Can SDMA be tested on its own?

While it’s technically possible, we don’t recommend it. SDMA results are most meaningful when interpreted alongside BUN, creatinine, and urinalysis. Most veterinary clinics offer these tests as part of a comprehensive kidney panel, which is the most cost-effective approach.

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References

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

[2] IRIS Staging of CKD (International Renal Interest Society) Guidelines, 2023 update

[3] Polzin DJ. Chronic Kidney Disease. Textbook of Veterinary Internal Medicine, 8th Ed