Contents

Urinalysis and Urine Culture

Indicators of infection from a urinalysis

- Turbid/cloudy urine

- Presence of > 10 WBCs

The presence of 10 WBCs per high-power field, upon microscopy, is equivalent to 100 cells/mm³ of urine, which is considered the upper limit of normal.

- Positive leukocyte esterase, which indicates the presence of WBCs in the urine.

- Presence of ≥ 10⁵ colony forming units (CFU) of bacteria per milliliter of urine.

Approximately one-third to one-half of young women with symptomatic lower urinary tract infections have less than 10⁵ CFU/ml of urine. Thus, the presence of ≥ 10² CFU/ml should be considered in the context of the patient characteristics and signs and symptoms.

- Positive nitrite test, which indicates the presence of a nitrate-reducing
microorganism, such as Escherichia coli.

- Elevated pH (6.5 – 8)

This is caused by organisms that produce urease, which catalyzes urea, producing
ammonia and carbon dioxide. Some of these organisms include Staphylococcus
saprophyticus, Klebsiella pneumoniae, and Proteus spp.

Urine Culture

A urine culture must ALWAYS be interpreted in the context of a urinalysis. Ideally, a urine culture would not be performed unless a urinalysis indicated a possible infection. If a patient has no signs of infection on urinalysis, no symptoms of infection, but a positive urine culture, the patient is most likely colonized with the organism, has asymptomatic bacteriuria, or the specimen was contaminated at the time of collection with organisms present on the skin/mucous membranes. Typically, catheterized patients will become colonized within 48 hours of catheterization. The only patient populations for which it is recommended to screen for and treat asymptomatic bacteriuria are pregnant women and patients scheduled for a genitourinary surgical procedure.