4) Observation of white-cell casts indicates renal tubular involvement in the inflammatory process. However, white cells in
casts rapidly degenerate to become granular casts. In our experience, white-cell casts are uncommonly observed in patients
with bacterial infections of kidneys. Therefore, absence of white-cell or granular casts does not exclude renal involvement
in the inflammatory process.
Interpretation of case scenario
A number of factors may have influenced the number of white cells in this Dachshund's urine sediment. Because the sample was
collected by the owner and therefore probably not fresh, a variable number of white cells might have disintegrated following
collection. Likewise, the alkaline pH of urine would enhance white cell disintegration. Because the sample was collected by
the owners during the voiding phase of micturition, some white cells could have originated from the genital tract. With these
factors in mind, what would you do next?
We elected to repeat the urinalysis on a sample collected by cystocentesis. The results were: specific gravity = 1.035; pH
= 6.5; protein = 1+; leukocyte esterase = negative; RBC in sediment = 2 to 4 per 450X; white cells in sediment = 5 to 10 per
450X. Culture of an aliquot of the cystocentesis sample revealed a significant number of Escherichia coli. These results confirm asymptomatic recurrent bacterial urinary tract infection. The site(s) of this UTI cannot be determined
on the basis of available information. The dog was subsequently treated with an antimicrobic based on susceptibility test
results. Bacterial culture of a urine sample collected by cystocentesis three days later resulted in no growth, although pyuria
was still present. A urine sample collected by cystocentesis two weeks after initiation of therapy was normal.
Dr. Osborne, a diplomate of the American College of Veterinary Internal Medicine, is professor of medicine in the Department
of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota.