Diagnosing Cat Urinary Infections
Urinary tract infections often go undiagnosed in cats. The diagnosis usually is made incidentally during a routine annual check-up. A urinalysis is a normal part of a thorough physical examination and is essential if kidney, bladder or other urinary tract disorders are suspected. It is easy and inexpensive to perform. The best way to collect feline urine is by “cystocentesis.” This involves inserting a needle through the cat’s abdominal wall, puncturing the bladder and aspirating a urine sample into a syringe. A cystocentesis takes only seconds to perform, can be done while the cat is awake and typically causes little to no noticeable discomfort. Occasionally, a fractious cat will require mild sedation. In rare cases, urine may be sampled through a urinary catheter, although this method has an increased risk of contamination and can be hard to perform. It is extremely difficult to collect urine from a cat by the “mid-stream free catch” method often used to get urine samples from dogs.
The actual urinalysis involves four simple steps: visual examination, chemical analysis, measurement of specific gravity and microscopic evaluation. The urine assessment should be done within one hour of collection. If that isn’t possible, the sample can be refrigerated and then returned to room temperature for later evaluation. The veterinarian will assess the color, cloudiness/clarity, volume, odor and overall appearance of the urine. She will immerse a reagent test strip called a “dipstick” into the sample and compare the color changes on the dipstick with standardized color-coded test pads. She will determine the specific gravity of the urine using a refractometer. “Specific gravity” is the weight of a substance compared to the standard weight of an equal amount of another substance – in the case of liquids, the standard usually is water. The final step in a urinalysis is to spin down (centrifuge) the sample and look at the resulting sediment under a microscope. This lets the veterinarian analyze parts of the urine that didn’t contribute to the chemical color changes on the dipstick and can reveal casts, crystals, white blood cells, bacteria, yeast and other infectious organisms that may be involved with a urinary tract infection. At each stage of the urinalysis, proper handling of the urine sample is essential to prevent contamination.
Further Diagnostic Procedures
Urine culture and sensitivity testing is the gold standard for diagnosing urinary tract infections in all species, including cats. Cultures should be performed on sterile samples obtained by cystocentesis, to reduce the risk of contamination. It is especially important to culture urine from cats with UTIs that are unresponsive to antibiotics. The urine sample normally is sent to an outside laboratory. The urine is placed on appropriate growth media and after several days is assessed for bacterial, fungal, viral or yeast growth. This information will help the cat’s veterinarian select the best course of therapy.
Routine blood work, including a complete blood count and serum chemistry profile, is often done as part of the initial diagnostic data base. While blood test results are not diagnostic of urinary tract infections, they may reveal underlying abnormalities that can contribute to UTIs, such as kidney disease, cancer or hyperadrenocorticism (Cushing’s disease). For recurrent or persistent UTIs, abdominal radiographs (X-rays) and ultrasonography can be helpful to evaluate the size and structure of the kidneys, ureters, bladder and urethra and to disclose abnormalities such as stones (uroliths), tumors and enlarged prostate glands, among other things. Radiographic contrast studies are available in many veterinary hospitals and are especially useful to identify kidney or bladder stones or masses that are obstructing the output of urine.
Urine cultures often are only performed if an initial course of broad-spectrum antibiotics does not resolve the infection. Unfortunately, the random administration of antibiotics, without first identifying the precise bacteria causing the infection, has contributed to the increasingly serious problem of antibiotic drug resistance in both human and veterinary medicine.