The CBC results are often normal with chronic pyelonephritis, but leukocytosis and neutrophilia with a left shift may be detected
in some dogs. The serum chemistry profile is usually normal unless chronic pyelonephritis is contributing to chronic renal
failure (azotemia with an inappropriate urinary specific gravity).
The urinalysis may reveal hematuria, pyuria, proteinuria, bacteriuria and leukocyte casts. Leukocyte casts are diagnostic
for renal inflammation and usually result from pyelonephritis. Remember that dilute urine specific gravity in dogs with nephrogenic
diabetes insipidus often occur secondary to pyelonephritis and absence of abnormalities does not rule out pyelonephritis.
Dogs with chronic pyelonephritis may have a negative urine culture and require multiple urine cultures to confirm urinary
tract infection. Ultrasonography and excretory urography are the preferred imaging procedures done for presumptively differentiating
between upper and lower urinary tract infection.
Ultrasonographic findings supporting pyelonephritis include dilation of the renal pelvis and proximal ureter and a hyperechoic
mucosal margin line within the renal pelvis and/or proximal ureter. Excretory urography may show dilation and blunting of
the renal pelvis with lack of filling of the collecting diverticula and dilation of the proximal ureter. In dogs with acute
pyelonephritis, the kidneys may be large; in dogs with chronic pyelonephritis, the kidneys may be small with an irregular
surface contour. Concomitant nephroliths may be seen in some dogs evaluated by survey radiography, ultrasonography or excretory
Definitive diagnosis requires urine cultures obtained from the renal pelvis or parenchyma or histopathology from a renal biopsy.
Pyelocentesis can be performed percutaneously using ultrasound guidance or during exploratory surgery. To confirm the diagnosis,
the biopsy specimen should include the renal cortex and medulla. Recurrent pyelonephritis may be asymptomatic.
Unresolved chronic pyelonephritis may lead to chronic renal failure and diagnostic follow-up, therefore, is important to document
resolution of the pyelonephritis. In dogs with nephroliths, resolution is unlikely unless the nephroliths are removed.
One should preferentially base the antibiotic selection on urine culture and sensitivity testing. Antibiotics used should
achieve good serum and urine concentrations and not be nephrotoxic. High serum and urinary antibiotic concentrations do not
necessarily ensure high tissue concentrations in the renal medulla; therefore, chronic pyelonephritis may be difficult to
cure. Do give orally administered antibiotics at full therapeutic dosages for at least four to six weeks. Do not use aminoglycosides
unless no other alternatives exist on the basis of urine culture and sensitivity testing. The trimethoprim/sulfa combinations
can cause significant side effects (keratoconjunctivitis sicca, blood dyscrasias, polyarthritis) when administered for more
than four weeks. Do urine cultures and urinalysis during antibiotic administration (approximately one week into treatment)
and one and four weeks after antibiotics are finished.
Dogs with pyelonephritis will usually return to normal health unless the dog also has nephrolithiasis, chronic renal failure
or some other underlying cause for urinary tract infection. Established infection of the renal medulla may be difficult to
resolve because of poor tissue penetration of antibiotics.
Dr. Hoskins is owner of DocuTech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200, or e-mail: firstname.lastname@example.org