Chronic Kidney Disease (CKD) in Dogs: Diagnosis, Testing & IRIS Staging Explained
Part 1 (this post): Diagnosis + testing + IRIS staging (and what to ask your vet)
Part 2: Nutrition myths, stage-appropriate feeding (including proteinuria vs non-proteinuria), what diets to avoid, and appetite support
Quick note: CKD care should be guided by your vet, ideally with a vet nutritionist for complex cases. My goal here is to help you understand the “why” behind the plan so you can advocate for your dog confidently.
What is CKD in dogs?
Chronic kidney disease (CKD) refers to progressive, irreversible changes to kidney structure and function over time. It differs from acute kidney injury (AKI), which develops suddenly and may be reversible.
CKD is managed — not cured — and early, structured intervention significantly improves quality of life and long-term outcomes.
How CKD is diagnosed (and why it’s never just one test)
CKD cannot be diagnosed from a single blood result.
International Renal Interest Society (IRIS) guidelines emphasise that staging should only occur in a stable patient, and that repeat testing is necessary to confirm chronicity and avoid misclassification (IRIS, 2023).
Veterinary teams are assessing patterns over time — not simply isolated numbers on one test.
Why multiple tests over time are essential for the bigger picture
CKD is a trend-based disease, not a snapshot disease.
Kidney biomarkers can fluctuate due to:
dehydration
recent illness
stress
infection
medication adjustments
changes in muscle mass (particularly in older dogs)
Creatinine, for example, is influenced by lean body mass. Dogs with muscle loss may have deceptively “lower” creatinine despite reduced kidney function (Hall et al., 2016).
This is one reason SDMA (symmetric dimethylarginine) is now used alongside creatinine. SDMA increases earlier in CKD and is less affected by muscle mass, making it a valuable complementary marker (Hall et al., 2016; Nabity et al., 2015).
However, even SDMA must be interpreted in context — which is why repeated measurements matter.
IRIS guidelines recommend that CKD staging be based on serial creatinine and/or SDMA values in a hydrated, stable patient, rather than a single abnormal result (IRIS, 2023).
Kidneys do not decline in a straight line
Longitudinal studies demonstrate that CKD progression varies significantly between individuals and may remain stable for extended periods before changing (Perini-Perera et al., 2021).
Serial testing allows vets to determine:
Whether kidney function is stable, slowly progressive, or rapidly declining
Whether an abnormal value was transient or persistent
Whether dietary or medical interventions are having measurable impact
Whether proteinuria is sustained
Whether blood pressure is consistently elevated or stress-related
Without repeated measurements, it is impossible to distinguish between:
early stable CKD
acute kidney injury
dehydration-related azotaemia
lab variation
This is not over-testing. It is pattern recognition medicine.
Chronic kidney disease is diagnosed and managed by trends over time — not by a single number on a single day.
The core components of CKD diagnosis
1. Clinical history and signs
Early CKD may present with:
Increased thirst and urination
Subtle weight loss
Reduced appetite
Mild nausea behaviours (lip licking, drooling)
These changes often precede dramatic lab shifts.
2. Blood tests: Creatinine and SDMA
Creatinine rises as glomerular filtration rate (GFR) falls, but it may not increase until approximately 50–75% of functional renal mass is lost (Nabity et al., 2015).
SDMA has been shown to increase earlier in CKD and correlates with declining GFR independently of muscle mass (Hall et al., 2016).
Using both markers together improves diagnostic accuracy (Nabity et al., 2015).
3. Urinalysis and urine concentrating ability
Urinalysis assesses:
Urine specific gravity (concentrating ability)
Sediment changes
Infection or inflammatory processes
Loss of urine concentrating ability often precedes significant azotaemia.
4. Proteinuria (UPC/UPCR)
Persistent proteinuria is an independent risk factor for CKD progression.
The ACVIM Consensus Statement on proteinuria confirms that sustained urinary protein loss is associated with worse outcomes and should be assessed via urine protein-to-creatinine ratio (UPC) (Lees et al., 2005).
Proteinuria is incorporated into IRIS substaging, reinforcing its prognostic value (IRIS, 2023).
5. Blood pressure
Systemic hypertension can both cause and accelerate kidney damage.
IRIS guidelines recommend regular blood pressure assessment alongside staging and substaging (IRIS, 2023).
Consistent trends over multiple readings are more clinically meaningful than one elevated in-clinic result.
6. Imaging
Ultrasound can help distinguish chronic structural change from acute causes and identify concurrent pathology such as obstruction or neoplasia. It can also be used in diagnosing CKD that occurs through renal dysplacia
IRIS Staging: What It Is (and What It Isn’t)
IRIS staging categorises CKD primarily based on:
Creatinine and/or SDMA concentrations
Followed by substaging based on proteinuria and blood pressure
Importantly, IRIS states that staging applies only to dogs with stable chronic kidney disease, not to patients with fluctuating acute values (IRIS, 2023).
This is precisely why repeat testing is so important before assigning a formal stage or implementing major dietary changes.
Key Takeaways from Part 1
CKD diagnosis relies on patterns over time, not single measurements
Creatinine and SDMA complement one another
Proteinuria and blood pressure significantly influence prognosis
Serial testing protects against misdiagnosis and inappropriate intervention
Accurate staging is the foundation of appropriate nutritional planning
References (Harvard Style)
Hall JA, Yerramilli M, Obare E, et al. (2016). Serum concentrations of symmetric dimethylarginine (SDMA) and creatinine in dogs with naturally occurring chronic kidney disease. Journal of Veterinary Internal Medicine, 30(3), 794–802. https://doi.org/10.1111/jvim.13942
IRIS (2023). IRIS Staging of CKD (modified 2023). International Renal Interest Society. Available at: http://www.iris-kidney.com
Lees GE, Brown SA, Elliott J, Grauer GE, Vaden SL. (2005). Assessment and management of proteinuria in dogs and cats: 2004 ACVIM Forum Consensus Statement. Journal of Veterinary Internal Medicine, 19(3), 377–385.
Nabity MB, Lees GE, Boggess MM, et al. (2015). Symmetric dimethylarginine assay validation and evaluation in dogs with chronic kidney disease. Journal of Veterinary Internal Medicine, 29(4), 1036–1044.
Perini-Perera S, et al. (2021). Evaluation of chronic kidney disease progression in dogs. Frontiers in Veterinary Science, 8, 621084. https://doi.org/10.3389/fvets.2021.621084
This article is provided for educational purposes only and is not intended to replace veterinary diagnosis, investigation or treatment.
Chronic kidney disease (CKD) requires formal diagnosis, staging and monitoring by a qualified veterinary surgeon. Accurate IRIS staging relies on serial blood and urine testing in a clinically stable patient, alongside blood pressure assessment and physical examination. No information within this article should be used to self-diagnose, delay veterinary consultation, or interpret laboratory results without professional guidance.
Sally Barker, The Canine Dietitian, does not diagnose medical conditions, prescribe medication, or replace veterinary opinion. Any nutritional discussion within this series is intended to support — not substitute — a collaborative veterinary care plan.
If your dog is showing symptoms such as vomiting, lethargy, reduced appetite, increased thirst, weight loss or changes in urination, please seek veterinary advice promptly.
