Evaluation of two bioluminescence-measuring instruments, the Turner Design and Lumac systems, for the rapid screening of urine specimens

Abstract

Two bioluminescence-measuring instruments, the Turner Design and Lumac systems, were compared with a standard plate culture method for their ability to rapidly screen 400 urine specimens. For cultures with less than 1,000 CFU/ml the Turner Design, with old and new evaluation formulas, gave 6.5 and 50.6% false-positive results, respectively, versus 17.6% at greater than or equal to 500 relative light units with the Lumac. For cultures which had greater than 10(5) CFU/ml the Turner Design gave 39% (old formula) and 14% (new formula) false-negative results compared with 4% at less than 200 relative units with the Lumac. The microorganisms most frequently isolated in the false-negative cultures from either system were gram-positive cocci. Predictive values for a positive test at greater than 10(5) CFU/ml were 77.4% (old formula) and 35.7% (new formula) for the Turner Design versus only 50% for the Lumac at greater than or equal to 500 relative light units. Predictive values for a negative test for both instruments were greater than 88% at greater than 10(5) CFU/ml. The Turner Design and Lumac systems were 4.0 and 3.7 times as expensive, respectively, as the plate culture method. Although both systems greatly reduce the time required to process urine specimens, their high costs as compared with that of plate culture, their failure to detect many specimens having greater than 10(5) CFU of gram-positive cocci per ml, and the numerous false-positives reported by both instruments suggest that additional improvements in the systems are warranted.