The urinary tract infection is one of the most common ailments in small animal practice yet many pet owners are confused about the medical approach. 

The urinary tract consists of the kidneys, ureters (tubes that carry urine to the bladder for storage), the urinary bladder, and the urethra that conducts 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, or UTI, we mean “bladder infection.”  

Because bladder infections are localized 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 does ascend all the way to the kidneys, then we may well 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. See the section on “Not So Simple Infections” below.)

It is also important to note that the term UTI in cats s frequently erroneously used to refer to feline idiopathic cystitis, which is a common inflammatory condition of the feline bladder affecting young adult cats. It is not a bladder infection.

Bladder Infection: What Does It Look Like And Where Did It Come From?

The kidneys make urine every moment of the day. The urine is moved down the ureters and into the bladder. The urinary bladder is a muscular little bag that stores the urine until we are ready to get rid of it. 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 that bacteria do not normally reside there. When bacteria (or any other organisms for that matter) gain entry and establish growth in the bladder, infection has occurred and symptoms can result. People with bladder infections typically report a burning sensation during urination. With pets we see some of the following signs:

  • Excessive water consumption.
  • Urinating only small amounts at a time.
  • Urinating frequently and in multiple spots.
  • Inability to hold urine the normal amount of time/apparent incontinence.
  • Bloody urine (though an infection must either involve a special organism, a bladder stone, a bladder tumor, or be particularly severe to make urine red to the naked eye).

Sometimes symptoms are hard to noice, so it is important to periodically screen patients at risk (such as elderly patients, patients with diseases like diabetes and patients that use cortisone-type medications long term).

A bladder infection is not contagious. Some important things to know:

  • Bladder infection is somewhat unusual in cats under age 10 years.
  • Bladder infection is less likely in neutered male dogs.

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 or not an infection is suspected. The urinalysis examines chemical 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 of the urine sediment to look for crystals, cells, or bacteria. This test often precedes the culture or lets the doctor know that a culture is in order. Indications that a culture of a urine sample should be done based on urinalysis findings include:

Graphic by MarVistaVet
  • Excessive white blood cells (white blood cells fight infection and should not be in a normal urine sample except as an occasional finding).

  • Bacteria seen when the sediment is checked under the microscope. (You would think that just confirming bacteria would confirm infection but, in fact, bacteria sometimes pass through urine without stopping and establishing an infection. Other criteria such as symptoms of inflammation and any white blood cells must be considered.)

  • Excessive protein in the urine (protein is generally conserved by the urinary tract. Urine protein indicates either inflammation in the bladder or protein-wasting by the kidneys. Infection must be ruled out before pursuing renal protein loss).

  • Dilute urine. When the patient drinks water excessively, urine becomes dilute and it becomes impossible to detect bacteria or white blood cells so a culture must be performed to determine if there are any organisms. Further, excessive water consumption is a common symptom of bladder infection and should be pursued.

  • If the patient has symptoms suggestive of an infection, a urinalysis need not precede the culture; both tests can be started at the same time.

Urine Culture (and Sensitivity)

This is the only test that can confirm a urinary tract infection. In this test, a tiny sample of urine is transferred to a specialized container and incubated for bacterial growth. This is like planting seeds in soil and seeing what kind of plants grow, if any.

Growth of bacteria on the culture plate confirms there is bacteria in the urine. In addition, once colonies of bacteria are growing, the type of bacteria can be identified, the number of colonies can be counted, and the bacteria can be tested for antibiotic sensitivity. Knowing the concentration of bacteria in the sample helps determine if the bacteria cultured might represent contaminants from the lower urinary tract or transient bacteria that are not truly colonizing the bladder. Similarly, knowing the species of bacteria also helps determine if the bacteria grown are known to cause disease or likely to be innocent bystanders. The antibiotic profile tells us what antibiotics will work against the infection. There is, after all, no point in prescribing the wrong antibiotic. 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.

There are different ways to collect urine. Talk to your veterinarian about the best way to collect the most accurrate sample from your canine or feline companion.

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