Laboratory in the diagnosis and management of urinary tract infections.

The laboratory is essential in the diagnosis and management of UTIs. The presence of pyuria and bacteriuria, the two most important indicators of UTIs, are most accurately determined by standard techniques. In quantitating pyuria, the finding of greater than or equal to 10 leukocytes/mm3 of urine by either hemocytometry or direct microscopy correlates highly with symptomatic, culture-proven UTIs. The determination of bacteriuria by direct microscopy is inaccurate, particularly at lower levels of bacteriuria; thus, quantitative urine cultures remain the most accurate measure of bacteriuria. Significant bacteriuria, previously defined as greater than or equal to 10(5) CFU/ml of urine, has been redefined with the observation that as few as 10(2) CFU/ml can be associated with significant pyuria and symptoms suggestive of cystitis. The need for routine and posttreatment urine cultures in nonpregnant women with acute dysuria remains controversial, but current data suggest that they are usually unnecessary. Rapid diagnostic tests for detection of pyuria and bacteriuria are designed to increase efficiency and decrease cost in the diagnosis of UTI. Unfortunately, none of these techniques can quantitate pyuria or bacteriuria as accurately as the standard methods, but the level of accuracy offered by the standard methods is not always necessary in the care of patients with uncomplicated UTIs. These tests are particularly well suited for screening asymptomatic high-risk populations. Noninvasive localization techniques continue to be explored as possible alternatives to invasive localization procedures, but they remain largely research tools that are not readily available to the practicing clinician. Understanding the applicability and appropriate use of newer technologies in the evaluation of patients with UTIs and how these technologies complement the standard diagnostic techniques will lead to better, more efficient, and less costly patient care.