However, protein can also enter urine because of urinary tract inflammation or bleeding, without primary damage to filtration. Small proteins are also normally filtered and then taken back up by the kidney tubules. The origin of the finding therefore needs investigation before it is considered a sign of permanent kidney disease.
When to see a vet urgently
An abnormal test result alone in a cat without symptoms is not usually an emergency, but these signs require prompt help:
- trying to urinate without passing any urine;
- difficulty breathing or sudden, painful paralysis of a hind leg;
- apparently sudden loss of vision or bumping into objects;
- severe vomiting, not eating or weakness affecting the cat's general condition.
Find a vet near you. Do not attribute these symptoms simply to proteinuria or wait for an already scheduled repeat sample.
Overview
Proteinuria in cats can be temporary, for example after stress or fever, or persistent, when it is associated with chronic kidney damage. It is most often detected in chronic kidney disease (CKD), glomerular diseases, amyloidosis or inflammatory conditions. The degree of proteinuria correlates with the severity and prognosis of kidney problems.
Even persistent proteinuria does not automatically mean advanced CKD. Protein loss through the kidneys can appear before kidney blood values rise. Conversely, many cats with CKD have little or no detectable proteinuria. The relationship between protein loss and prognosis concerns kidney disease assessed as a whole; a single reading cannot show how much life a cat has left.
Causes
- Kidney-related causes:
- glomerulonephritis,
- renal amyloidosis,
- chronic kidney disease,
- diseases of the kidney tubules.
- Factors outside the kidneys:
- fever, stress and physical exertion,
- systemic inflammatory and infectious diseases,
- tumours.
- Postrenal causes, involving the urinary tract:
- inflammation of the bladder, urethra or renal pelvis.
In practice, causes are divided into prerenal, renal and those involving protein added to urine later. For example, a high blood concentration of haemoglobin or muscle-derived myoglobin can increase urinary protein. In this situation, the abnormality does not begin with leakage from a glomerulus. In bladder inflammation, protein may enter with inflammatory material.
Inflammation of the renal pelvis is located within the kidney, so it should not be interpreted as a lower urinary tract condition alone, despite its grouping in the list. Inflammation, blood and the collection method are considered before a UPC result is used to measure renal protein loss.
Risk factors
- Older cats, particularly those with chronic kidney disease.
- Cats with a viral infection, such as FeLV or FIV.
- Breed predisposition: Abyssinians and Siamese have a tendency towards amyloidosis.
- Cats with chronic inflammatory diseases.
This risk list does not mean that breed or viral infection alone confirms renal proteinuria. Information about general proteinuria risks in cats is limited. Even the organ affected by amyloidosis varies: kidney-predominant disease is recognised in Abyssinians, while liver amyloidosis is also a major problem in Siamese and Oriental cats. Proteinuria can nevertheless occur in non-pedigree cats too.
Typical symptoms
Proteinuria itself usually causes no obvious symptoms and is detected by urine testing. However, a cat may show:
- lethargy and reduced appetite;
- weight loss;
- thirst and increased urination in chronic kidney disease;
- swelling and ascites with severe protein loss in nephrotic syndrome;
- signs of the underlying disease, such as infection, inflammation or tumours.
The appearance of urine does not reliably reveal its protein content. Normal colour and usual urination habits do not rule out the finding. Conversely, straining in the litter tray or blood in the urine prompts investigation of the urinary tract; neither symptom in itself establishes glomerular disease.
Drinking more, weight loss and reduced appetite may be associated with kidney disease or other illnesses. Monitor these changes, but do not restrict drinking to reduce urine volume. High blood pressure can accompany kidney disease and damage organs such as the eyes, so even a cat without symptoms may need its blood pressure measured.
Complications and consequences
- progression of chronic kidney disease;
- development of nephrotic syndrome, involving swelling, low albumin and high blood lipid levels;
- blood clots with marked proteinuria;
- a poorer prognosis for kidney disease.
Nephrotic syndrome and blood clots are particularly associated with significant protein-losing kidney disease, rather than every small dipstick finding. Albumin is a blood protein that helps keep fluid within blood vessels. When large amounts are lost, fluid can accumulate in tissues or the abdominal cavity. This requires a broader assessment than simply repeating the urine protein measurement.
Proteinuria is one measure of kidney disease risk and progression. Kidney function, blood pressure and nutritional status are monitored alongside it. A low value alone does not guarantee mild disease, and a high value does not prove that all the protein comes from the glomeruli.
Diagnosis at the vet
- routine urinalysis to detect protein;
- quantitative assessment using the urine protein-to-creatinine ratio, or UPC;
- blood biochemistry, including urea, creatinine, albumin and lipid levels;
- kidney ultrasound to identify structural changes;
- bacterial urine culture to rule out infection;
- kidney biopsy if glomerular disease or amyloidosis is suspected.
A dipstick is a screening tool. Its protein pad reacts particularly to albumin, and the result is interpreted alongside urine concentration and other findings. Cleaning product residue in a sample container can interfere with the result. The sample should therefore be collected in a clean, suitable container and delivered according to the practice's instructions.
Urine sediment is examined to assess cells, bacteria and other material. Clear inflammation or bleeding can prevent the UPC being interpreted specifically as kidney protein leakage. The need for bacterial culture is decided according to the situation; a protein finding alone does not mean antibiotics are needed. The sample may be repeated after another abnormality has been investigated.
What does the UPC show?
The UPC compares urine protein with urine creatinine, reducing the effect of urine dilution. In feline CKD substaging, a result below 0.2 is non-proteinuric, 0.2–0.4 is borderline and above 0.4 is proteinuric. These thresholds are used alongside other investigations; they are not a diagnosis or the same medication instruction for every cat. Repeat samples confirm whether a renal finding persists.
Blood creatinine, other kidney function markers, albumin and blood pressure complete the assessment. Ultrasound shows structure but does not replace urine testing. Kidney biopsy is considered selectively, for example in suspected glomerular disease if tissue information could change treatment. Bleeding risk and procedural safety are assessed before sampling. Not every patient with proteinuria needs a biopsy.
Treatment and follow-up
Treatment targets the origin of the finding. A urinary tract infection, blood pressure problem and persistent renal protein loss require different approaches. Suspected glomerulonephritis does not automatically mean immunosuppressive medication: possible infection and other underlying causes are investigated first. Amyloidosis and inflammatory glomerular disease are not treated on the same assumption either.
Persistent renal proteinuria in a cat with stable CKD may be treated with a diet suitable for kidney disease and medication to reduce protein leakage. These medicines act on the hormonal system regulating pressure within the kidneys. Dehydration and unstable kidney function are considered before treatment starts. Treating high blood pressure may itself reduce proteinuria.
Borderline cases need monitoring and individual judgement. There is no clear evidence of benefit from medication to reduce protein leakage specifically in borderline cases. A medicine is therefore not prescribed simply because a result lies between the reference range and clear proteinuria. You should not add protein to the diet or sharply restrict it to correct a urine result either.
Feeding and safe medication
A kidney diet is chosen according to the whole clinical picture and introduced while ensuring your cat continues eating. Adequate nutrition is important; do not withhold food to force acceptance of a new diet. Water must be freely available. The diet aims to manage kidney disease and is not promised to correct every cause of proteinuria.
After medication is started or changed, your cat's condition, blood pressure, creatinine and potassium are monitored, followed later by UPC trends. Blood pressure that is too low, raised potassium or worsening kidney values may require a treatment change. Report new weakness, vomiting or loss of appetite to the treating practice. Do not combine or change medicines yourself.
What are check-ups aiming to achieve?
A fall in UPC may indicate a good response if your cat's condition and kidney function remain stable. A single lower reading is not enough if general health worsens at the same time. Comparison takes account of inflammation or blood in samples and the timing of measurements. The interval between check-ups is agreed according to the starting situation and treatment used.
Prevention
- Arrange regular urine and blood tests, particularly for an older cat.
- Treat urinary tract infections promptly.
- Keep your cat at a healthy weight and provide a complete, balanced diet.
- Avoid uncontrolled use of medicines that can harm the kidneys.
- Monitor viral infections through FeLV and FIV testing.
Lifestyle measures cannot prevent every disease of the glomeruli or other tissues. Planned samples can nevertheless help identify a persistent change and an underlying cause needing treatment. Monitoring is also useful when your cat appears healthy but the cause of the finding remains uncertain.
Important for cat owners
Proteinuria is a laboratory finding that often indicates hidden kidney damage. Remember that even if your cat looks healthy, regular urine testing can reveal a problem early. The earlier kidney damage is identified, the better the chance of slowing disease progression and extending your cat's life.
This article provides general information and does not replace veterinary care. If you notice signs of illness in your cat, contact a vet.
Frequently asked questions
Does protein in urine always mean kidney failure?
No. Protein can also enter urine because of inflammation, bleeding or another cause. Even renal proteinuria can occur before kidney blood values rise. The source and persistence of the finding are investigated separately.
Why does the urine sample need repeating?
One sample does not always distinguish a temporary change from a persistent one. Repeat testing can track changes and assess the result when factors such as inflammation or blood no longer interfere with interpretation.
Does a borderline UPC need medication?
Not automatically. A borderline result is considered alongside other kidney findings and blood pressure. Monitoring is needed, but the benefit and safety of medication are assessed individually.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- 2026 iCatCare consensus guidelines on the diagnosis and management of chronic kidney disease in cats, iCatCare / Journal of Feline Medicine and Surgery, accessed 2026-11-03.
- Reassessment of normal values in dogs and cats with chronic kidney disease, International Renal Interest Society, accessed 2026-11-03.
- Chemical constituents, Cornell University / eClinpath, accessed 2026-11-03.
- Glomerulonephritis in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Chronic Kidney Disease, Cornell University College of Veterinary Medicine, accessed 2026-11-03.
- Hypertension, Cornell University College of Veterinary Medicine, accessed 2026-11-03.
- Amyloidosis in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Blocked Bladder in Cats, PDSA, accessed 2026-11-03.
- IRIS Staging System, International Renal Interest Society, accessed 2026-11-03.