Overview
Chronic Kidney Disease is the most common renal disorder in geriatric dogs and cats. It involves irreversible structural damage to nephrons, leading to a progressive decline in glomerular filtration rate (GFR). By the time clinical signs appear, 75% or more of nephrons are typically non-functional — making early detection through biomarkers (creatinine, SDMA) critical. The International Renal Interest Society (IRIS) provides the staging framework used worldwide. CKD is distinguished from Acute Kidney Injury (AKI) by its insidious onset, chronic nature (>3 months), and non-azotemic early stages. Treatment focuses on slowing progression, managing complications (proteinuria, hyperphosphatemia, acidosis, anemia), and maintaining quality of life.
IRIS CKD Staging
Staging requires two consecutive measurements ≥3 months apart to confirm chronicity. A minimum database (creatinine, SDMA, urinalysis, blood pressure) is required for proper staging.
| Stage | Creatinine (Dog) | Creatinine (Cat) | SDMA | Clinical Picture |
|---|---|---|---|---|
| Stage I | <1.4 mg/dL | <1.6 mg/dL | <18 µg/dL | Non-azotemic. Normal creatinine. Often an incidental finding or imaging finding. No clinical signs. Requires urinalysis and blood pressure assessment. |
| Stage II | 1.4–2.8 mg/dL | 1.6–2.8 mg/dL | 18–35 µg/dL | Mild azotemia. May see subtle PU/PD. Mild weight loss. Often still eating normally. Conservative management begins. |
| Stage III | 2.9–5.0 mg/dL | 2.9–5.0 mg/dL | 36–54 µg/dL | Moderate azotemia. Clinical signs common: vomiting, weight loss, dehydration, PU/PD, anorexia. Full intervention warranted. |
| Stage IV | >5.0 mg/dL | >5.0 mg/dL | >54 µg/dL | Severe azotemia. Uremic signs prominent: severe vomiting, oral ulceration, marked depression, seizures possible. End-of-life discussions often warranted. |
Common Clinical Signs
Diagnostic Approach
A complete staging workup includes hematology, biochemistry with SDMA, urinalysis with UPC ratio, blood pressure measurement, and abdominal imaging.
| Diagnostic Test | Expected Findings in CKD |
|---|---|
| Serum Creatinine | Elevated — the cornerstone of IRIS staging. Must be interpreted with BUN, USG, and SDMA. Creatinine is kidney-function dependent but is influenced by muscle mass — cachectic animals may be understaged. |
| SDMA (Symmetric Dimethylarginine) | Elevated — more sensitive than creatinine, becoming abnormal when GFR declines by only ~25% (vs ~75% for creatinine). SDMA is not affected by muscle mass. Ideal for early detection. IRIS cutoffs: ≥18 µg/dL (dog/cat) = abnormal. |
| BUN (Blood Urea Nitrogen) | Elevated, but less specific than creatinine (affected by diet protein, GI bleeding, dehydration, catabolism). BUN:Creatinine ratio >20:1 suggests prerenal or GI bleeding component. |
| Urinalysis | Inappropriatively dilute urine (USG <1.030 dog, <1.035 cat) despite azotemia — key finding distinguishing CKD from prerenal azotemia. Proteinuria on dipstick should be quantified with UPC. Sediment exam for casts (renal) and bacteria (UTI). |
| UPC Ratio | Proteinuria quantification. IRIS recommends categorizing as non-proteinuric (<0.2 dog, <0.4 cat), borderline (<0.3 / <0.6), or proteinuric (>0.3 / >0.6). Proteinuria is independently associated with faster CKD progression — ACE inhibitor therapy indicated. |
| Blood Pressure | Hypertension is common — especially in cats (up to 65% of CKD cats). Target <160 mmHg systolic. Uncontrolled hypertension causes further renal damage and risks retinal/ cerebral hemorrhage. Amlodipine is first-line for cats. |
| CBC | Normocytic, normochromic, non-regenerative anemia (decreased erythropoietin production). More pronounced in Stage III-IV. PCV typically 20-30% in CKD patients. May see mild leukocytosis if concurrent infection or inflammation. |
| Abdominal Ultrasound | Kidneys may appear small, irregular, with increased echogenicity, loss of corticomedullary distinction. Not required for diagnosis but helps rule out obstructive uropathy, pyelonephritis, and renal neoplasia. |
Differential Diagnoses
- Acute Kidney Injury (AKI) — Acute onset (hours to days), severe azotemia, often toxin/drug-associated. History is key. AKI can also occur as an acute decompensation of CKD ("acute on chronic kidney disease"). Two creatinine measurements ≥3 months apart = CKD vs AKI.
- Prerenal azotemia — Elevated creatinine/BUN from dehydration or hypovolemia. USG will be concentrated (>1.030 dog, >1.035 cat). Responds to fluid therapy. CKD: dilute urine persists despite azotemia.
- Hyperadrenocorticism (Cushing's Disease) — PU/PD is prominent; may cause mildly elevated creatinine. Low-dose dexamethasone suppression or ACTH stimulation differentiates. Cushing's causes muscle wastage but kidney size is usually normal on ultrasound.
- Diabetes Mellitus — PU/PD is prominent. Glucose and fructosamine differentiate from CKD. May see concurrent diabetic nephropathy.
- Bacterial Urinary Tract Infection / Pyelonephritis — May cause azotemia and PU/PD. Positive urine culture differentiates. White blood cell casts in urine sediment suggest pyelonephritis.