Urinary tract infections are quite common in dogs. (They’re uncommon in cats, but a lot of cats get treated with antibiotics for non-infectious urinary tract disease.) An important aspect of managing urinary tract infections (UTIs) is getting a proper diagnosis. Diagnosing a UTI involves a few different things:
- Clinical signs: Does the animal have signs that indicate something abnormal is going on in the bladder? This can include frequent urination, abnormal urination, straining to urinate or similar problems.
- Cytological: When a urine sample is examined under the microscope, are there changes consistent with an active infection, like the presence of large numbers of white blood cells and red blood cells?
- Culture: Can bacteria be grown from the urine sample?
Culture is very important to help determine if a UTI is really present. It’s also very important for determining the best treatment, especially since antibiotic resistant bacteria are becoming more common. A baseline culture is also useful if the infection comes back, as it provides information about whether the first bug was not actually eliminated or whether re-infection other bacteria has occurred. Differentiating these two situations is important for determining subsequent treatment as well as the need for additional testing to see if there are any underlying reasons for recurrent infections.
Culture is also something that can be done improperly. If a person has or may have a UTI, that person will usually be asked to collect your own "mid-stream" urine sample by collecting urine into a sterile cup part-way through urination, so that any superficial bacterial contaminants get flush out before the sample is collected. That’s not so easy to do in dogs and cats. Collecting midstream free-flow samples into a sterile container without the sample being contaminated by the pets hind end or haircoat, or by the person doing the collecting, is very difficult. A contaminated sample can result in misleading conclusions and potentially inappropriate treatment. Getting a proper sample is critical.
There are two main ways to deal with this problem:
1) Look at the kinds and number of bacteria grown from the urine culture. General guidelines (that are completely empirical) give cutoffs for the level of bacterial growth that should be considered clinically significant versus incidental contamination, with a grey-zone in between. This can be tough to interpret with confidence, so while looking at bacterial numbers can provide some information, it’s not the preferred approach.
2) Collection of a sample by cystocentesis. This is a very quick, simple and low risk procedure that involves taking a sample directly out of the bladder using a needle and syringe. The animal is placed on it’s back (no anesthesia required, and usually even sedation is unnecessary), the skin is cleaned, and a thin needle is passed through the lower part of the belly, where the bladder lies directly under the skin. Often, if an ultrasound machine is available, a quick check is performed to see the size and location of the bladder, but the procedure can be done without ultrasound assistance.
While cystocentesis may seem like a big deal for collection of a fluid that the pet passes freely on a regular basis, it provides much better information and is largely considered the standard for urine collection in dogs and cats. Unless there is a medical reason not to do it, cystocentesis should be used for collection of urine samples for culture.
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