Introduction
Urinary tract infections in dogs are usually diagnosed through urinalyses and blood tests. In complicated cases of persistent or recurrent infection, radiographs (x-rays), ultrasound examination and urine culture may be appropriate additional diagnostic tools.
Diagnosing Dog Urinary Infections
Urinalysis
A routine urinalysis is one of the most valuable tests available to veterinarians as an indicator of canine health or disease. It is a normal part of thorough routine examinations and is critical in cases of suspected renal, bladder or other urinary tract disorders. Urinalysis is easy and inexpensive to perform and involves 4 major steps once the urine sample is obtained: visual examination, chemical analysis using dipsticks, measurement of specific gravity and microscopic examination and analysis of the urine.
The preferred method of collecting urine is by cystocentesis, which involves inserting a needle through the abdominal wall, puncturing the bladder and removing the sample by aspiration through a syringe. However, for routine urinalyses, most veterinarians perform the procedure on a freshly voided urine sample collected mid-stream in a clean, dry, sterile container. Urine can also be collected through a catheter. The assessment should be done within one hour of collection, regardless of collection method; if that is not practical, the sample should be refrigerated and then returned to room temperature at the time of the examination.
First, the veterinarian will assess color, turbidity/clarity, volume, odor and overall appearance by visual inspection. Next, she will immerse a multi-test reagent strip into the urine and compare the reactions on the dipstick with different test pads, followed by assessing the specific gravity of the urine using an instrument called a refractometer. The next step is to centrifuge (“spin down”) the sample and examine the centrifuged sediment under a microscope to analyze those parts of the urine that do not contribute to the chemical reagent strip changes. At each stage of the urinalysis, proper handling of the specimen is essential. The results of these procedures will provide an enormous amount of information to the veterinarian, including the urine pH, protein, glucose, ketones, bilirubin, blood, nitrites and other chemical component levels that reflect function or dysfunction of kidneys and other organs. Microscopic assessment provides information about whether the urine contains physical abnormalities such as casts, crystals, bacteria, white blood cells, yeast or other organisms, many of which can be diagnostic of urinary tract infections or other disorders.
Urine Culture
Urine culture and sensitivity are the “gold standard” for diagnosing urinary tract infections. Cultures should be performed on sterile samples preferably obtained by cystocentesis to reduce chances of contamination. Culture is also highly recommended for infections treated with but unresponsive to antibiotics. The urine is placed on appropriate growth media and after several days will be assessed for bacterial, fungal, viral or yeast growth, depending upon which organism is suspected. Different growth media are required for different organisms. The laboratory will identify the particular organism(s) involved, enabling the veterinarian to select the appropriate course of therapy.
Testing for Underlying Conditions
Routine blood work (complete blood count and serum chemistry profile) is normally done as part of the initial diagnostic data base, together with the urinalysis. The blood test results may suggest a predisposing condition or disease that is contributing to the urinary tract infection, such as renal disease, neoplasia or hyperadrenocorticism (Cushing’s disease). For recurrent or persistent UTIs, abdominal radiographs (x-rays) can be used to look for uroliths (stones), enlarged prostate or other abnormal sediment in the bladder. Abdominal ultrasound is helpful to assess the structure of the kidneys, urinary bladder and urethra. Urinary contrast studies are available in many veterinary hospitals as well.