Urine is the specimen most frequently submitted for culture. It also presents major problems in terms of proper specimen collection, transport, culture techniques, and interpretation of results. As with any other specimen submitted to the laboratory, the more information provided by the submitting physician the more able is the laboratory to provide the best possible culture data.
The most common sites of urinary tract infection (UTI) are the urinary bladder (cystitis) and the urethra. From these sites the infection may ascend into the ureters (ureteritis) and subsequently involve the kidney (pyelonephritis). Females are more prone to infection of the urinary tract and also present the greater problem in the proper collection of specimens.
In both males and females, UTI may be asymptomatic, acute, or chronic. Asymptomatic infection can be diagnosed by culture. Acute UTI is more frequently seen in females of all ages; these patients are usually treated on an outpatient basis and are rarely admitted to hospital. Chronic UTI in both males and females of all ages is usually associated with an underlying disease (e.g., pyelonephritis, prostatic disease, or congenital anomaly of the genitourinary tract) and these patients are most often hospitalized. Asymptomatic, acute, and chronic UTI are three distinct entities and the laboratory results often require different interpretation.
Asymptomatic pyelonephritis in females may go undetected for some time, and is often only diagnosed by carefully performed quantitative urine culture. Chronic prostatitis is common and difficult to cure, and is often responsible for recurring UTI. In most UTI, irrespective of type, enteric bacteria are the etiological agents, Escherichia coli being isolated far more frequently than any other organism. In about 10% of patients with UTI, two organisms may be present and both may contribute to the disease process. The presence of three or more different organisms in a urine culture is strong presumptive evidence of improper collection or handling of the urine specimen. However, multiple organisms are often seen in UTI in patients with indwelling bladder catheters.