Protein in dog urine – causes, UPC tests and treatment

Overview

A finding, rather than one disease

Even healthy dogs have a little protein in their urine. Albumin is the most common protein excreted in urine. Albuminuria specifically means albumin in urine. Proteinuria can also involve other proteins.

Proteinuria with a UPC above 0.5 has been found in 11–13% of apparently healthy older dogs. This figure concerns the older dogs studied and does not describe the risk for all dogs. Protein loss through the kidneys can occur while blood creatinine is still normal. The finding therefore helps identify some kidney diseases before obvious kidney failure develops.

Causes

How does protein reach the urine?

The glomerulus is a kidney filter that normally prevents most blood proteins entering the urine. Small kidney tubules reabsorb proteins that have passed through the filter. Glomerular damage increases protein passage. Tubular disease, in turn, reduces protein reabsorption. This can occur in conditions such as Fanconi syndrome and leptospirosis.

Bladder inflammation, urinary stones or a urinary tract tumour can add protein to urine after it leaves the kidneys. Prostate or uterine inflammation can also affect protein findings in a urine sample.

If the blood contains unusually large amounts of small proteins, these can exceed the tubules' reabsorption capacity. A plasma cell tumour, for example, may produce such immunoglobulin light chains. Red blood cell breakdown and severe muscle injury can also cause a protein load originating before the kidneys.

Antibody complexes or deposits of an abnormal protein called amyloid in glomeruli can increase protein passage. Kidney inflammation or a tumour can also cause protein leakage.

Protein excretion can increase temporarily with strenuous exercise, fever or a seizure. However, ordinary exercise should not automatically be blamed: 20 minutes of moderate treadmill exercise did not change albuminuria in dogs.

Risk factors

Dogs with chronic kidney disease are also tested for urinary protein loss. High blood pressure can increase glomerular filtration pressure and protein leakage. Cushing's disease and administered glucocorticoid medication have been associated with proteinuria.

Inherited familial nephropathy in Cocker Spaniels damages the glomerular basement membrane. Associated proteinuria and progressive kidney disease can become apparent between 6 months and 2 years of age. A single protein finding does not, however, mean your dog has this particular inherited disease.

Infections and inflammatory diseases can be associated with glomerular protein leakage.

Typical symptoms

Proteinuria may be found in a urine sample at a health check without changes visible at home. Any signs depend on the underlying disease. Observations may include:

• Swelling of the legs or underside of the chest.
• Swelling around the abdomen.
• A temporary dent left after pressing a swollen area.
• Difficulty breathing because of fluid in the chest or abdominal cavity.
• Increased drinking and urination with impaired kidney function.
• Loss of appetite, weight loss and vomiting as kidney disease progresses.

Tiredness can occur particularly once kidney disease reaches the uraemic stage. These are consequences of the underlying disease or severe protein loss, rather than signs accompanying every positive urine sample.

Advanced kidney disease can also cause diarrhoea and mouth ulcers.

Complications and consequences

Albumin loss and blood clots

Severe protein loss can reduce blood total protein and albumin concentrations. Nephrotic syndrome also involves high cholesterol. Fluid can accumulate beneath the skin and in the chest and abdominal cavities.

Blood clots have been found in 12–21% of studied dogs with glomerular disease. An individual dog's clot risk cannot be reliably predicted from albumin concentration or the amount of proteinuria.

In chronic kidney disease, greater protein loss is associated with a poorer outlook. In one study of dogs with kidney disease, those with a UPC above 1.0 had around 3 times the relative risk of uraemic crisis and death compared with dogs with lower values. This describes an association between groups, rather than a particular dog's remaining lifespan.

Protein-losing kidney disease can also involve high blood pressure.

High blood pressure can damage the eyes, central nervous system and heart.

Diagnosis at the vet

Assessing the sample and protein amount

Initial tests include urinalysis, UPC, a blood count and blood biochemistry. Urine sediment is examined for findings including inflammatory cells, red blood cells and bacteria. The cause of visible blood or inflammatory cells in urine is investigated before assessing renal proteinuria further. Urine culture investigates possible bacterial infection if needed. A sample collected directly from the bladder by needle reduces contamination by genital secretions.

Urine dipsticks are useful for screening but can give false positives. In dilute urine, they may also miss small amounts of albumin. UPC means the protein-to-creatinine ratio measured in the same urine sample. This ratio reduces variation caused by urine concentration. A single-sample ratio reflects daily protein excretion without collecting a full day's urine.

An older comparison examined 599 canine urine samples. Dipsticks detected albuminuria with 81% sensitivity. Their specificity for identifying unaffected samples in dogs was only 48%. These figures describe that test comparison and explain the need for quantitative confirmation.

A sensitive albumin assay may be used selectively in a young dog at risk of inherited protein-losing kidney disease. It can detect small amounts of albumin when a routine screening test remains negative.

What does the UPC result mean?

For classifying renal proteinuria, a canine UPC below 0.2 means non-proteinuric. A value of 0.2–0.5 is borderline. A value above 0.5 is classified as proteinuric. However, a laboratory's general reference may be below 0.5. A result within the laboratory reference can therefore fall into the borderline clinical category.

Ideally, classification uses at least 2 urine samples over at least 2 weeks. Collecting 3 samples over 2 weeks is also used. Day-to-day variation is why a single result in a dog without signs is checked again. Persistent borderline proteinuria is reassessed within 2 months. After excluding causes outside the kidneys, a UPC above 2.0 strongly suggests glomerular disease.

Investigating the underlying cause

Your dog is allowed to settle before blood pressure measurement, and classification is based on several readings.

Blood pressure is measured in persistent proteinuria. Infection testing is targeted according to where your dog lives and their travel history. Abdominal ultrasound can look for a tumour associated with proteinuria. Kidney biopsy is considered if tissue sampling could establish the disease type and change treatment. Procedure risks and the sample's special handling requirements are considered.

Treatment

Treating the cause and reducing protein loss

Your vet targets treatment to the identified cause. Successful treatment of a urinary tract infection, for example, can resolve associated proteinuria. Persistent renal proteinuria is treated when UPC exceeds 0.5, regardless of kidney disease stage.

An angiotensin receptor blocker, or ARB, is used to treat protein loss through the kidneys. An appropriate veterinary renal diet is used. An ACE inhibitor may be used selectively as part of treatment. Combining medicines requires particular care and close kidney function monitoring. Dehydration is corrected before starting an ACE inhibitor or ARB, as kidney filtration could otherwise deteriorate rapidly.

Protein-losing kidney disease may require medication to prevent blood clots. Immunosuppressive treatment is considered in certain severe glomerular diseases. It is not started solely because of a positive urine dipstick.

Treatment response and duration

A UPC below 0.5 is unattainable for many dogs with primary glomerular disease. A 50% reduction from the initial UPC may then be the target. A good response includes stable blood creatinine, falling UPC and, where relevant, a rise in previously low albumin. Falling UPC alone can also reflect loss of functioning kidney units as disease progresses. The result is therefore interpreted alongside changes in blood creatinine and SDMA.

With ACE inhibitor treatment, blood pressure, creatinine and potassium are usually checked 1–2 weeks after starting or changing treatment. The UPC response is often checked at around 1 month. These are monitoring times, rather than medicine course lengths. Treatment of chronic renal protein loss usually continues for life unless the underlying cause resolves.

Prevention

Disease-specific breeding plans can reduce the risk of inherited kidney disease. To prevent familial nephropathy in Cocker Spaniels, some breed guidelines require at least one parent of a litter to be tested or clear by inheritance for FN.

Urine monitoring in older dogs can reveal hidden protein loss before signs become visible at home. Free access to water helps prevent dehydration in dogs with kidney disease. Identifying a treatable underlying disease is also part of managing protein loss. Not all causes of renal proteinuria can be prevented through home care.

Where possible, medicines harmful to the kidneys are withdrawn following veterinary assessment in dogs with kidney disease.

Important for dog owners

Monitoring at home and at the practice

Keep UPC results with dates and the corresponding creatinine, SDMA, albumin and blood pressure results. Record changes in appetite, drinking, urination, weight and swelling. Bring a medication list, including any glucocorticoid treatment. Its use can be associated with increased protein excretion.

Follow your sampling instructions. Bacterial contamination of a urine sample can affect UPC. Report when and how the sample was taken, and any blood, fever or unusual exertion. Ask whether the finding has been confirmed as renal and persistent, what treatment aims to achieve and when safety checks are due. Contact your vet if your dog becomes ill during medication and stops drinking or eating normally. A dehydrated dog needs reassessment of the safety of treatment affecting kidney blood flow.

Frequently asked questions

Does protein in urine always mean kidney failure?

No. Proteinuria can result from urinary tract inflammation or bleeding, for example. Even renal protein loss can occur with normal blood creatinine. Tests investigate both the protein's origin and kidney function, so a positive urine dipstick alone does not establish the whole diagnosis.

Can a finding in a dog without signs be left unmonitored?

Persistent renal protein loss needs investigation even in a dog without signs. A borderline UPC is checked again within 2 months. Repeat sampling distinguishes a temporary change from a persistent finding and identifies a cause needing treatment before general condition deteriorates.

What does a borderline UPC mean?

The borderline UPC range for dogs is 0.2–0.5. However, the laboratory reference may be below 0.5. The result is therefore assessed alongside clinical classification, other urine findings and repeated measurements. Borderline does not mean either definitely normal or glomerular disease requiring immediate treatment.

Can diet help with protein loss?

A veterinary renal diet forms part of treatment for confirmed renal protein loss. Renal diets have been found to improve UPC in dogs receiving medication for proteinuria. However, a single protein finding is not a reason to devise a severely protein-restricted homemade diet yourself; the cause must be investigated first.

Can proteinuria resolve completely?

A protein finding associated with a urinary tract infection, for example, may disappear after successful infection treatment. Treatment of chronic renal protein loss, by contrast, may continue for life. The response is assessed using kidney function and albumin as well as UPC so a reduction in protein is interpreted in context.