Sunday, March 15, 2009

Crystals and Bacteria in a Cat or Dog's Urine

Dear Dr Gordon: On a recent well-pet check at my vet, the urine analysis from the lab revealed that both my cat and dog have crystals in the urine and bacteria. Both my pets are happy and healthy. How significant is this? BK

Dear BK: First of all, crystals and bacteria in the urine MAY BE a significant medical problem, OR may be nothing at all. What do I mean by this?

Should You be Concerned About Crystals and Bacteria In Your Pet's Urine?

Many veterinarians utilize veterinary reference laboratories to analyze blood, urine, stool, and other samples. If urine is collected on a pet that is completely asymptomatic for any urinary problems (no straining to urinate, no blood, no unusual urinary behavior) and submitted to a laboratory for analysis, the presence of crystals in that particular urine sample may have formed en route to the lab.

How is this possible? Sometimes crystals can form from the time the urine was collected to the time it was read at the lab due to changes in temperature and changes in the pH of the urine. Crystals that were soluble in solution at the time of collection can actually crystallize out in the solution over time. Is this significant? In a pet that is symptomatic, crystals in the urine are significant. If the pet is completely asymptomatic, then the crystals are probably not a significant issue. However, a fresh urine sample should always be re-examined at the veterinarian's office to make sure crystals are not present immediately after collection. If crystals are present in a fresh sample, these are a real finding and should be addressed. There can be many causes for the formation of crystals. Diet, genetic predisposition, and bacterial infection are some of the culprits. 

How Is A Urine Sample Collected?

The presence of bacteria in the urine can sometimes also be misleading. Veterinarians collect urine in a variety of ways. The best way to collect a urine sample is by a technique called cystocentesis. In this technique, the pet is allowed to build up urine in the urinary bladder and the urine is extracted from the bladder in a sterile fashion. This is usually done by cleansing the area of any surface bacteria on the skin and collecting the urine with a very fine hypodermic needle and syringe. If bacteria are found on this "sterile" collection technique, it is always significant. Sometimes when veterinarians are faced with a particularly uncooperative patient, we will ask that the owners collect a urine sample for us. Even though we hope the sample is collected a aseptically as possible, we realize that collection in this way is less than ideal, and will probably be contaminated to some degree. Almost any sample that is collected at home, by the owner, either by a "mid stream catch" (in the case of a big dog or via the litter box (in the case of cats) will be contaminated. Even though we realize this, it is important to analyze the urine anyway since other findings in the urine may be significant. We can still discern many important facts about the pet's health status from a urine sample collected by the owner. Significant findings could be sugar in the urine, crystals in a fresh sample, the presence of inflammatory cells or cancer cells, protein in the urine, and/or blood in the urine. All of these would be present regardless of how the urine was collected.

Is There Bacteria or Not?

Sometimes there actually will be the presence of bacteria, but the lab or veterinarian reports that no bacteria were seen. How is this possible? Sometimes the bacteria numbers are very small, or sometimes a very dilute urine will not show any presence of bacteria when examined under the microscope (although they are there). If the doctor suspects that bacteria may be present causing symptoms, and "no bacteria seen" is reported by the lab, he or she may recommend a culture and sensitivity be done on the urine.

How To Collect It Correctly?

To do a culture and sensitivity correctly, the sample should be collected straight from the urinary bladder to avoid environmental contamination. Once the urine is collected, it is transferred to a sterile test tube for transport to the lab. Once the urine arrives at the lab, special procedures are employed to enhance the growth of any bacteria that could be present. This involves placing the urine in a test tube containing a special broth to enhance the reproduction of any bacteria found in the urine. After the bacteria are grown in the broth, the bacteria is identified and this solution is "streaked across" a special plate containing another type of growth media. Special small discs, each impregnated with a different antibiotic, are then spread onto this plate. The growth pattern of the bacteria helps determine which antibiotic(s) would be effective in killing the bacteria.

As you can see, there is a big difference in the reporting and interpretation of crystals and bacteria in the urine. DrG

For more information on Urinary Crystals click here to visit

Author:  Dr. David Gordon, Holistic Veterinarian
Original post: 3/15/09
Updated: 4/29/24