Dr. Gary Edelson, DVM
In dogs and cats, the urinary tract consists of the kidneys, ureters (tubes that carry urine to the bladder for storage), the urinary bladder, and the urethra that transports urine outside the body. A urinary tract infection could involve any of these areas though most commonly, when we speak of a urinary tract infection (commonly referred to as a UTI or bladder infection). With a simple urinary tract infection confined to the bladder, there are rarely signs of infection in other body systems (no fever, no appetite loss, and no change in the blood tests). If the infection ascends to the kidneys, then we do tend to find other signs and other lab work changes. While a kidney infection is technically also a urinary tract infection, we usually use the term pyelonephritis to describe a kidney infection.
How do dogs and cats get a bladder infection?
The kidneys are constantly making urine every moment of the day, then the urine is moved down the ureters and into the bladder. The urinary bladder is a muscular little pouch that stores the urine until it is ready to be voided. The bladder must be able to expand for filling, contract down for emptying, and respond to voluntary control.
The bladder is a sterile area of the body, which means there is no bacteria present in the bladder. When bacteria enter, and establish growth in the bladder, infection has occurred and symptoms can result.
The external genital where urine is voided is not sterile and therefore has bacteria present. Bladder infections often occur when bacteria from the genitals climb (ascend) into the bladder by overcoming the pet’s natural defense mechanisms. Certain diseases and conditions can make urinary tract infections more complicated such as: kidney infections (pyelonephritis, bladder stones, bladder tumors, anatomic abnormalities, vaginal structures and prostatitis)
Common urinary tract infection symptoms include:
- Excessive water consumption
- Urinating small amounts at a time
- Urinating frequently
- Inability to hold urine the normal amount of time/apparent incontinence.
- Blood in the urine
Sometimes there are no symptoms at all, so it is important to periodically screen patients at risk (such as elderly patients and patients that use cortisone-type medications long term). In addition, certain diseases like diabetes can make pets more prone to urinary tract infections.
The external genital area where urine is expelled is teeming with bacteria. Bladder infection results when bacteria from the lower tract climb into the bladder, defeating the natural defense mechanisms of the system (forward urine flow, the bladder lining, inhospitable urine chemicals etc.). A bladder infection is not contagious.
Testing for Bladder Infections
There are many tests that can be performed on a urine sample and people can get confused about what information different tests provide.
The urinalysis is an important part of any database of laboratory tests. It is an important screening tool whether an infection is suspected and with newer technologies can even be performed at home using Petnostics. The urinalysis examines properties of the urine sample such as the pH, specific gravity (a measure of concentration), and amount of protein or other biochemicals. It also includes a visual inspection (either under a microscope or use of new technology, Sedivue, of the urine sediment to look for bacteria, crystals, casts, red blood cells, white blood cells, or other types of cells. A urinalysis is the first test performed and can sometime determine if a culture of the urine is needed. If the following are noted, a urine culture is recommended:
- Excessive white blood cells (these cells help fight infections)
- Excessive protein in the urine (protein is generally conserved by the urinary tract. Urine protein indicates either inflammation in the bladder or protein being loss by the kidneys. Infection must be ruled out before pursuing kidney protein loss)
- Dilute urine. When the patient drinks water excessively, urine becomes dilute and it becomes harder to detect bacteria or white blood cells so a culture must be performed to determine if there are any organisms. Additionally, excessive water consumption is a common symptom of bladder infection, but can also be a sign of many other disease processes.
Urine Culture (and Sensitivity)
Bacterial culture and sensitivity of urine is performed to identify the offending organism (usually E. coli, Proteus, Staph or Strep). Urine for culture must be obtained by cystocentesis (collection of urine by a sterile needle passed through the abdominal wall and into the bladder) with the aid of an ultrasound machine or catheterization (collection of urine via a catheter passed by sterile technique through the urethra and into the bladder), to assure proper interpretation of results. This is the only test that can confirm a urinary tract infection. The antibiotic profile tells us what antibiotics will work against the infection. Clearly, the culture is a valuable test when infection is suspected. Urine culture results require at least a couple of days as bacteria require this long to grow.
A free catch sample is easily obtained by catching urine mid-air as it is passed. The sample may be contaminated by the bacteria of the lower urinary tract but will not be contaminated by the floor or another environmental surface. Using a urine collector or in cats, hydrophobic cat litter (won’t absorb the urine) can make collecting a urine sample a breeze.
At the veterinarian’s office, there are additional ways (catherization and cystocentesis) to collect urine for culture and sensitivity testing as the sample must be sterile. There are four ways to collect a urine sample: table top, free catch, catheter, and cystocentesis.
With the catheter technique, a small tube is passed into the bladder and the sample is obtained. This is not the most comfortable method for the patient though the procedure is quick. One drawback is bacteria can be introduced into the bladder accidentally but fortunately, this is a rare.
The ideal collection method is cystocentesis where a needle directly inserted through the abdomen and into the bladder using an ultrasound for guidance in most cases. Occasionally a little blood enters the sample during the needle stick but for culture purposes, the sample can be considered pristine.
Consult your veterinarian before making changes to any monitoring or treatments.
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