Diagnosing Urinary Tract Infections in Dogs
Canine urinary tract infections (UTIs) are usually easy to diagnose, although they frequently are diagnosed incidentally when a dog is brought in for another problem. The veterinarian will take a thorough history and perform a complete physical examination, no matter what the dog’s presenting problems are. Most of the time, the initial evaluation will involve taking blood and urine samples for routine assessment. Many UTIs are diagnosed when the urinalyses results come in, even though the dog may have shown no recognizable signs of having a urinary tract infection. The blood test results may suggest a predisposing condition or disease, such as renal disease, neoplasia (cancer) or Cushing’s Disease.
Microscopic evaluation of a dog’s urine – called a urinalysis - is one of the most valuable diagnostic tools to assess overall canine health. Most veterinarians recommend a urinalysis as part of an annual check-up. A urinalysis is easy and inexpensive to perform. It involves four basic steps, once the urine sample is collected: visual examination, chemical analysis, measurement of urine specific gravity and microscopic assessment.
The preferred method of collecting urine is called cystocentesis. Cystocentesis involves inserting a sterile needle through the belly wall into the urinary bladder, and removing a urine sample by aspiration into a syringe. For routine tests, most veterinarians take a freshly voided urine sample collected mid-stream in a dry, sterile container. Urine can also be collected through a catheter, although this is not commonly done. Urine should be assessed within one hour of collection, regardless of the collection method. If that is not practical, the sample should be refrigerated and then returned to room temperature.
The veterinarian will assess the urine’s color, clarity, volume, odor and overall appearance. She will immerse a multi-test reagent strip into the sample and compare the chemical reactions with those of different test pads, based on color changes. She will assess the specific gravity of the urine using an instrument called a refractometer. The next step is to centrifuge the sample and examine the centrifuged sediment microscopically, to analyze those parts of the urine that do not contribute to the chemical reagent strip changes. The urinalysis results can provide an enormous amount of diagnostic information, including the urine pH (acidic or alkaline) and the levels of protein, glucose, ketones, bilirubin, blood, nitrites and other substances in the urine that reflect function or dysfunction of the kidneys and other organs. Microscopic assessment of urine can reveal whether it 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.
The gold standard for diagnosing urinary tract infections is culture and sensitivity. Cultures should be performed on sterile samples ideally obtained by cystocentesis, to reduce the chance of contamination. Culture is also highly recommended for infections that are treated with but unresponsive to antibiotics. For complicated, recurrent, resistant or persistent UTIs, abdominal radiographs (X-rays) can be useful to identify uroliths (calculi, stones), enlarged prostate (prostatomegaly) or 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 and can help to visualize masses or other obstructions along the course of the urinary tract.