Urine colony counts or quantification of urine cultures determines the number of bacterial colonies per mL of urine. This is helpful in assessing whether the bacteria isolated and identified on culture are possible contaminants, normal flora, or significant pathogens. Results are reported as the number or range of colony forming units (cfu) per mL of urine, along with identification of the organism and its antimicrobial sensitivity (see table).

Interpretation of Quantitative Urine Cultures*

*cfu/mL urine, NA=not applicable

Cultures on liquid urine are useful to diagnose or rule out UTI from conditions such as: vaginitis, prostatitis, urolithiasis, pyelonephritis, urethritis, ureteritis, vesicoureteral reflux, congenital disorders (e.g. ectopic ureter), trauma, chronic renal failure, endocrine disorders (e.g. Cushing's disease, diabetes mellitus), and neoplasia.

In a recent study of 101 dogs with hyperadrenocorticism, diabetes mellitus, or both disorders, 42% had UTI diagnosed by urine culture. UTI was present in 46% of dogs with hyperadrenocorticism, 37% of dogs with diabetes mellitus, and 50% of dogs with both disorders. E. coli was the most common bacterium isolated, present in 69% of dogs. Clinical signs of dysuria or pollakiuria were present in <5% of the dogs with UTI, and 19% of dogs with positive cultures had neither pyuria or bacteriuria on urinalysis.

Senior pets often have occult UTI. Of 90 clinically normal geriatric dogs studied at VCA West Los Angeles Animal Hospital in 1998 and 1999, 12 dogs had UTI in the absence of any clinical signs of lower urinary tract disease (LUTD).

Although UTI are an uncommon cause of LUTD in cats, urine culture should be performed in cats with multiple episodes, in those that have perineal urethrostomies or have been catheterized, and those with urine specific gravity <1.035.

Chronic renal failure is a risk factor for UTI in cats, as up to 30% of cats with this disease have UTI. Similarly, according to Dr. Dennis Chew at Ohio State University, cats with perineal urethrostomies have a >50% incidence of UTI. Hence, cats with chronic renal failure or perineal urethrostomies should have urine cultures performed periodically to permit early detection of UTI.

Urinalysis should be performed on freshly collected urine for any animal with suspected urinary tract disease, and for routine health screening of geriatric pets. Cystocentesis is the preferred method of urine collection, whenever possible. Urine for culture should be submitted in a sterile red top tube (RTT), not a serum separator tube. Only a small volume of urine (˜0.5 mL) is needed. A separate container of urine should be submitted for routine urinalysis. Clients are encouraged to send a separate, sterile urine sample, along with each urinalysis, in case it is decided that an Add-On urine culture is needed.

Copan swabs of urine or urine submitted in broth are not preferred for urine culture, and enable reporting only of semiquantitative culture results.

As a general rule, pets should be off antibiotics for at least 48-72 hours prior to urine culture. However, urine cultures performed during antibiotic treatment for UTI (without stopping antibiotics) can be used to assess treatment efficacy.