Internal Medicine Update: Proteinuria

Internal Medicine Update
Central Toronto Veterinary Referral Clinic
Michael Goldstein DVM, Diplomate ACVIM (Small Animal Internal Medicine)

Proteinuria

Although dogs and cats normally have small amounts of protein in their urine, persistent and increased protein concentrations are abnormal and termed proteinuria. Several studies have shown that proteinuria is linked to a worse prognosis in both azotemic and non-azotemic cats and dogs, and so reducing proteinuria improves survival in dogs. Proteinuria is classified into three groups:

  1. Pre-renal: low-level proteinuria, including hemoglobin, myoglobin, and Bence Jones proteins from neoplastic plasma cells
  2. Renal: caused by abnormal renal handling of normal plasma proteins and sub-classified as:
    1. functional: occurs in response to certain transient phenomena-sepsis, stress, hypo/hyperthermia, mild and transient
    2. Pathological: associated with a defect in the glomerulus, tubule, or interstitium
      1. glomerular: most persistent and highest levels (UPCs >2), amyloidosis, glomerulonephritis
      2. tubular: persistent but low grade, i.e. Fanconi’s syndrome
      3. interstitial: transient and mild, leakage from capillaries around the tubules, inflammatory diseases (i.e. Leptospirosis, pyelonephritis, and renal neoplasia)

Proteinuria seen on three serial urine tests ≥ 2 weeks apart with a normal sediment could be indicative of pathologic renal proteinuria.

UPC Value Substage
Dog Cat
<0.2 <0.2 Non-Proteinuric
0.2 to 0.5 0.2 to 0.4 Borderline
>0.5 >0.4 Proteinuric

The traditional “dipstick” method is the first screening test to have a high sensitivity for albumin but is subject to false positive results. If the dipstick is at all positive then a quantitative assessment with a urine protein:creatinine ratio (UPC) is required. The UPC is the gold standard for quantitative assessment of proteinuria in dogs and cats and has been highly correlated with 24-hour protein loss (a specific update on UPCs to follow).http://www.iris-kidney.com

My general rule is that a urinalysis including a semi-quantitative protein evaluation (dipstick) should be performed on every dog and cat for which routine blood work is indicated. A complete blood count, chemistry panel, urine culture, and blood pressure should be performed. In dogs, tick-borne disease titers, heartworm test, abdominal ultrasound, and testing for hyperadrenocorticism should be considered. Leptospirosis titers should be considered in dogs with acute proteinuria. In cats, FeLV and FIV screening, feline pancreatic lipase level, or imaging and thyroxin measurement should be considered if the animal is over four years, based on signalment, history, and physical examination.

The goal of treatment should be to achieve the lowest level of proteinuria possible: ideally >50% reduction in proteinuria in dogs and greater than 90% reduction in cats. Diet has a large effect on the magnitude of proteinuria, and several studies have documented the therapeutic value of a specially formulated diet in the management of chronic kidney disease, including amelioration of renal secondary hyperparathyroidism, decreased incidence of uremic crisis, and increased survival. These diets typically contain conservative amounts of high quality protein, adequate non-protein calories, and are restricted in phosphorus. Angiotensin converting enzyme (ACE) inhibitors have been shown to reduce proteinuria and slow the progression of renal injury in proteinuric subjects. Although studies in cats have shown reductions in proteinuria with the use of ACE inhibitors, they have not demonstrated a clear benefit in terms of survival or reduced likelihood of developing azotemia. This is in contrast to dogs and humans, which have shown a decreased risk in progressive azotemia and increased survival. Angiotensin II receptor antagonists (ATRA): Losartan is the most commonly used angiotensin II receptor blocker in small animals, but limited data exist on its use in dogs or cats. There are new products arriving in the veterinary market and so we hope to see new data in the next few years. Anticoagulants: Low dose acetylsalicylic acid (aspirin) should be considered as an adjunct therapy for protein-losing nephropathies. Coagulation parameters should be evaluated to help guide the decision to use these drugs.

Dr. Michael Goldstein is a Board Certified Small Animal Internist, and is part of the Team at the Central Toronto Veterinary Referral Clinic. He is available for referrals from Monday to Friday. Please contact him with any questions in Internal Medicine by phone (416-784-4444) or email (michaelgoldstein@ctvrc.ca)

Emergency Veterinarian Toronto

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