Detection of bacteriuria by leukocyte esterase, nitrite, and the automicrobic system

The predictive value for detection of significant bacteriuria was determined for use of the Chemstrip leukocyte esterase-nitrite dipstick (LN) and the Vitek Automicrobic System (AMS) using a conventional culture method (CM) as the reference procedure. The predictive values for positive and negative tests for detection of greater than or equal to 10(5) bacteria/mL for LN testing alone (2,782 specimens), AMS testing alone (729 specimens), and AMS testing of only LN positive specimens (253 specimens) were 29% and 97%, 67% and 99.5%, and 74.7% and 99.4%. The low predictive values for positive AMS tests were the result of discrepancies in enumeration in which counts of 10(4)/mL by CM often were classified as 10(5)/mL by AMS. Screening of specimens by LN reduces the cost of subsequent processing of LN positive specimens. Processing of LN positives by CM yielded the lowest total cost. Processing of LN positives by AMS resulted in the lowest labor cost.