Proteinuria has received renewed attention as a factor impacting the progression of cases of canine and feline chronic renal failure (CRF) and as a marker of early renal disease. Primary renal disease, as well as various infectious, inflammatory, metabolic and neoplastic disorders can damage glomerular vasculature and cause leakage of albumin into the glomerular filtrate, even in subclinical stages. Microalbuminuria (MA), the persistence of small amounts of albumin in the urine, is an early indicator of primary renal disease, lower urinary tract disease, or the presence of some other underlying disease causing early renal damage. Detection of MA during a routine health examination provides veterinarians with a new tool to help identify these situations.

Protein traffic across the glomerular barrier primarily involves albumin, and is influenced by many factors, including: damage to glomerular basement membrane, glomerular capillary hemodynamics, and endothelial cell dysfunction. The appearance of protein in urine is also influenced by proximal tubular cell function, as these cells normally reabsorb and degrade any filtered protein, thereby reducing the amount appearing in urine.

Common causes of MA can be classified as glomerular and post-glomerular. Glomerular causes of MA arise from altered glomerular membrane permeability, occurring either from glomerular injury or glomerular capillary hypertension. The ensuing leakage of albumin into the glomerular filtrate exceeds tubular capacity to reabsorb or degrade the excess albumin. Post-glomerular causes of MA include: failure of renal tubules to degrade or reabsorb filtered albumin (e.g., acute or chronic tubulointerstitial disease), or hemorrhage and/or inflammation of the lower urinary tract.

The trace amounts of albumin in urine detected by MA testing (1 to 30 mg/dL) are below the limits of protein detected by conventional urine dipsticks. Urine albumin concentrations above this limit are classified as overt proteinuria and can often be detected by measuring the protein:creatinine ratio. Antech's newly introduced reference MA test is a species-specific immunoassay, which correlates very closely to results obtained with the Heska ERD Healthscreen™ Urine test in clinical studies.

Several studies have evaluated the prevalence of MA. In one study, the prevalence of MA in 86 dogs whose owners were not seeking veterinary care was 19%, whereas it was higher (36%) in 159 dogs whose owners were seeking veterinary care. In another study, the prevalence of MA was 30% in dogs evaluated for health problems at a Veterinary Teaching Hospital. A third study of 3041 staff-owned dogs from over 350 veterinary clinics, found an overall MA prevalence of 24.7%. There was a statistically significant correlation between increasing age and the presence of MA. For example, MA was present in 7.4% of dogs > 3 years old, 8.6% of dogs 3-5 years of age, 20% of dogs 6-8 years of age, 36% of dogs 9-11 years of age, and 49.1% of dogs 12 years of age and older. These findings appear to support previous reports of an increased incidence of glomerular disease in older dogs. Lastly, the overall prevalence of MA of 1243 staff-owned cats from veterinary clinics was 24.5%. Similar to the dog study, there was a statistically significant correlation between increasing age and the presence of MA in geriatric cats. For example, MA was present in 35.5% of cats 12-15 years of age and 72.7% of cats 16-23 years of age.