Protein-losing nephropathy (PLN) in dogs is a progressive glomerular disease in which the kidneys abnormally leak protein into the urine, leading to low blood protein, fluid accumulation, clotting complications, and eventual kidney failure.
Bernese Mountain Dogs, Soft-Coated Wheaten Terriers, and Cocker Spaniels carry breed-specific genetic risk; early detection via urine protein-to-creatinine ratio (UPC) testing is critical because PLN can be silent until advanced.
Last reviewed: June 2026
What Causes Protein-Losing Nephropathy?
Protein-losing nephropathy results from damage to or dysfunction of the glomerular filtration barrier — the specialized structure in kidney filtration units that normally retains large proteins (especially albumin) in the bloodstream. When this barrier is disrupted, proteins escape into the urine in abnormally large quantities. The underlying causes span immune-mediated glomerulonephritis (most common), hereditary nephropathy, amyloidosis, and glomerular damage secondary to systemic diseases such as Lyme nephritis, leishmaniasis, neoplasia, or chronic infections.
As described in Ettinger's Textbook of Veterinary Internal Medicine, the clinical consequence of sustained protein loss is hypoalbuminemia — low blood albumin — which reduces oncotic pressure and allows fluid to leak from blood vessels into body cavities (ascites, pleural effusion) and tissue (peripheral edema). Concurrently, PLN creates a hypercoagulable state: the loss of anticoagulant proteins through the diseased glomeruli promotes thromboembolic events (pulmonary embolism, mesenteric vein thrombosis, renal vein thrombosis), which are a leading cause of acute deterioration and sudden death in PLN dogs.
Signs: From Subtle to Severe
The insidious onset of PLN means dogs may appear healthy for months or years while significant protein loss is occurring. By the time clinical signs appear, hypoalbuminemia and glomerular injury may be substantial. Early signs include: mild lethargy, reduced appetite, and occasionally foam in the urine (visible protein in urine). As hypoalbuminemia worsens, more overt signs emerge: abdominal distention (ascites), weight loss despite normal appetite, swollen limbs (peripheral edema), and respiratory difficulty from pleural effusion.
Approximately 30–50% of dogs with PLN develop hypertension (systolic blood pressure greater than 160 mmHg), which further accelerates glomerular damage. As described in Nelson & Couto's Small Animal Internal Medicine, dogs with urine protein-to-creatinine ratio (UPC) above 2.0 on at least two samples taken 2 weeks apart meet the threshold for significant proteinuria requiring investigation. A UPC above 5.0 indicates severe proteinuria associated with higher risk of thromboembolic events.
The ACVIM Consensus Statement on Proteinuria, 2005 distinguishes pre-renal, renal, and post-renal causes of proteinuria and sets investigation thresholds that guide when kidney biopsy and treatment escalation are warranted.
Diagnosis and Monitoring
Diagnosis begins with repeated urine protein-to-creatinine (UPC) ratio measurement. A single elevated UPC must be confirmed on a second sample 2 weeks later because transient proteinuria from urinary tract infection, exercise, or stress can mimic PLN. Once confirmed, additional diagnostics include: complete chemistry panel, complete blood count, urinalysis and culture, blood pressure measurement, chest and abdominal radiographs or ultrasound, and potentially kidney biopsy to identify the underlying glomerular lesion.
Kidney biopsy (ultrasound-guided) is often recommended because the underlying histological type (membranous nephropathy, membranoproliferative GN, amyloidosis, focal segmental glomerulosclerosis) influences prognosis and treatment selection. Referral to a veterinary internist or nephrologist is advisable. Monitoring every 2–4 weeks initially, then every 1–3 months once stable, is standard — tracking UPC, albumin, blood pressure, BUN, creatinine, and SDMA. Initial workup typically costs $500–1,200; kidney biopsy adds $1,000–2,500.
Treatment
Treatment targets are: slow glomerular damage progression, manage hypertension, reduce thromboembolism risk, and address the underlying cause if identifiable. ACE inhibitors (enalapril, benazepril) or angiotensin receptor blockers reduce intraglomerular pressure and slow protein loss; they are first-line therapy for most PLN dogs regardless of underlying cause. Blood pressure must be monitored closely after starting these agents.
Antiplatelet therapy (aspirin at low doses, clopidogrel) is often used to reduce thromboembolism risk — one of the most life-threatening complications. Dogs with serum albumin below 2.0 g/dL are at particularly high thromboembolism risk and may warrant heparin or low-molecular-weight heparin in acute settings. Dietary protein restriction is generally not recommended in PLN — unlike CKD without proteinuria — because these dogs are losing protein and need adequate intake to maintain body mass; however, sodium restriction is important for edema management.
When to See a Vet
Call your vet today if:
- Foamy urine noticed on multiple occasions
- Abdominal swelling, fluid accumulation, or unexplained weight gain (ascites)
- Swollen legs or paws (peripheral edema)
- Labored breathing (possible pleural effusion)
- Your dog's breed carries PLN genetic risk (Bernese Mountain Dog, Soft-Coated Wheaten Terrier, Cocker Spaniel)
Go to the ER immediately if:
- Sudden acute respiratory distress
- Sudden hindlimb weakness or paralysis (aortic or spinal thromboembolism)
- Collapse, rapid breathing, or pale gums (pulmonary embolism)
- Seizures with known hypoalbuminemia
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Frequently Asked Questions
What breeds are most at risk for protein-losing nephropathy? Bernese Mountain Dogs, Soft-Coated Wheaten Terriers, English Cocker Spaniels, and Doberman Pinschers have documented hereditary predisposition to PLN. Breed-specific screening (annual UPC testing from 1–2 years of age) is recommended for these breeds. Labrador Retrievers with concurrent Lyme disease also have elevated PLN risk.
How is PLN detected before symptoms appear? A urine protein-to-creatinine ratio (UPC) test on a free-catch urine sample is the primary screening tool. A UPC above 0.5 in dogs warrants repeat testing; above 2.0 confirmed on two samples warrants full evaluation. Routine annual urinalysis at wellness visits catches early PLN before hypoalbuminemia develops.
How much does PLN treatment cost? Monthly ACE inhibitor medication costs $20–80. Blood pressure monitoring and bloodwork run $150–350 per visit every 1–3 months. Kidney biopsy adds $1,000–2,500. Dogs requiring hospitalization for complications (thromboembolism, severe edema) face costs of $1,500–5,000 per episode. Long-term management averages $2,000–6,000 per year.
Can PLN be cured? PLN caused by an identifiable underlying disease (Lyme nephritis, systemic lupus) may improve significantly if the underlying condition is treated successfully. Hereditary and idiopathic immune-mediated forms are rarely curable, but progression can be slowed significantly with ACE inhibitors, blood pressure control, and monitoring. Median survival from diagnosis varies widely: 2 months to 3+ years depending on cause and severity.
Is PLN the same as protein-losing enteropathy? No — protein-losing enteropathy (PLE) involves protein loss through the intestinal wall (often from inflammatory bowel disease or lymphangiectasia), while PLN involves protein loss through the kidneys. Both cause hypoalbuminemia and edema, but the diagnostic workup and treatment differ. A vet can distinguish them with urinalysis, UPC, and intestinal evaluation.
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