Proteinuria in the dog: a clinicopathological study in 51 proteinuric dogs

In 51 dogs with predominantly massive urinary protein loss, the daily loss was quantified and glomerular and tubulointerstitial lesions from renal biopsies were characterised and graded using histology, immune fluorescence and electron microscopy. The highest median daily urinary protein loss occurred in dogs with membranous glomerulonephritis (median 380 mg kg-1 d-1) and renal amyloidosis (median 257 mg kg-1 d-1). Although in nine febrile dogs the urinary protein loss was transient, both glomerular and tubular lesions were diagnosed in five and seven of these dogs, respectively. The pattern of urinary proteins was determined using sodium dodecyl-sulphate polyacrylamide gel electrophoresis. The albumin fractional clearance (FC) was raised in 46 dogs, whereas the FCS of the low molecular weight (MW) protein fraction (MW less than 66,000) and high molecular weight protein fraction (MW more than 66,000) were raised in 42 and 28 dogs, respectively. Both the high molecular weight protein FC and albumin FC significantly correlated to the grade of glomerular lesions, whereas the low molecular weight protein FC only moderately significantly correlated to the grade of tubular lesions. The selectivity index, calculated as (formula; see text) did not differentiate between the various forms of glomerulopathies. The urinary lysozyme concentration was significantly correlated to the grade of tubular lesions. It is concluded that although quantitative and qualitative measurements of urinary proteins can provide additional clinical information, they do not have a reliable predictive value and histopathological examination of renal tissue is still necessary for the final diagnosis.