Laboratory diagnosis of urinary tract infection in ambulatory women.

We evaluated the accuracy and work load of six different approaches to identifying urinary tract infections in a general microbiology laboratory. Midstream urine (MSU) specimens from 387 ambulatory women were examined for pyuria and were cultured using a dual-plating technique that detects both low (10(2) to 10(4) organisms per milliliter) and high (greater than or equal to 10(5) organisms per milliliter) colony counts. Seventy-four urinary tract infections (defined as greater than or equal to 10(5) organisms per milliliter of MSU or greater than or equal to 10(2) aerobic gram-negative bacilli per milliliter of MSU in symptomatic patients) were identified. Twenty-four (32%) of the infections were characterized by low colony counts and would not have been identified using a 10(5) or greater colony-forming units/mL criterion for infection. Using the presence of pyuria to direct microbiological processing of urine specimens was the most accurate and efficient method of identifying urinary tract infections among voided specimens from ambulatory women, particularly if rapid screening methods for pyuria can be used.