Laboratory detection of urinary tract infections
The high incidence of negative urine specimens submitted for microbiologic evaluation (80% in many settings) and the clinical advantages offered by early preliminary results have led to intense efforts over many years to develop rapid, accurate and relatively inexpensive alternatives to standard culture techniques. This review has touched on some of the techniques that range from the very simple to the complex and automated. All are relatively rapid compared to the standard culture time of 24 hours. The newer automated methods are generally accurate as well. The method used should take into account the prevalence of infection in the population to be screened, the number of urines to be screened daily, ancillary laboratory support available and the particular setting in which the specimens are collected. Many of the automated methods are cost effective primarily in a setting where the expense of the equipment can be offset by savings in personnel time achieved by excluding negative specimens from further processing. It is important to be aware of the limitations of the test employed as well as the definitions used in the test to define significant bacteriuria. Many of the screens evaluated in this review are most useful and rapid when using the standard definition of > 105 cfu/ml of bacteria but may need more extensive evaluation if lower counts such as > 102 cfu/ml are considered clinically important. When the ordering physician is interested in the full evaluation of urines that have less than 105 cfu/ml, it may be necessary to inform the lab to allow longer screening time or to set up conventional cultures.
