Microalbuminuria: When to Test

In dogs and cats, urine albumin concentration in the range of 1 to 30 mg/dL is called microalbuminuria (MAlb). MAlb may have preglomerular, glomerular, or postglomerular causes. Patients should be tested for MAlb only when pre- and postglomerular causes of proteinuria/albuminuria have been excluded. Selected abstracts and studies suggest that the following patients do not benefit from MAlb testing or should not undergo MAlb testing until underlying causes are identified and treated: those with pyuria, bacteriuria, or lower urinary tract disease; hyperglobulinemia that may be due to neoplasia; a urine protein-creatinine ratio (UPC) already shown to be increased; and owners unwilling to do further diagnostic testing based on MAlb test results when the pet is healthy. Patients that may benefit from testing include those with renal failure and dipstick proteinuria but normal UPC; dog breeds with a high prevalence of glomerular disease; patients with diseases known to cause glomerular injury and in which therapy might be considered if they are MAlb positive but still UPC negative; and patients in which occult disease is more likely and whose owners would be willing to pursue further diagnostics if the MAlb test result is positive. Unfortunately, it is still unclear when or how much further investigation is warranted when MAlb is diagnosed, although patients with positive results should first have UPC ratios obtained to quantitate the severity of proteinuria. It is likewise unknown whether therapeutic intervention benefits dogs with MAlb.

COMMENTARY: Proteinuria has become an increasingly important consideration in veterinary medicine. The common use of the UPC ratio and the availability of sensitive, specifies-specific albumin assays have revolutionized our approach to this problem. While it remains to be established whether protein leak causes kidney injury, it is well accepted that proteinuria is a marker for kidney disease and a negative prognostic indicator. Therapies that reduce proteinuria in animals with chronic kidney disease are generally renoprotective. A remaining issue is how to handle patients with persistent, isolated microalbuminuria (repeated positive results for albumin in urine in a dog or cat with no other known abnormalities). This article describes an approach to such patients that emphasizes several of the advantages (and challenges) associated with these highly sensitive and specific tests and their utility for monitoring subsets of our patients, particularly those at risk for developing chronic kidney disease.

Microalbuminuria: Which patients should I test and when? Pressler BM. NAVC PROC 2009, pp 780-781.