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 <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-500 relative light units with the Lumac. For cultures which had >105 CFU/ml the Turner Design gave 39% (old formula) and 14% (new formula) false-negative results compared with 4% at <200 relative light 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 > 105 CFU/ml were 77.4% (old formula) and 35.7% (new formula) for the Turner Design versus only 50% for the Lumac at .500 relative light units. Predictive values for a negative test for both instruments were >88 % at >105 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 > 105 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.

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The authors have evaluated the MS-2 (Abbott) and Lumac (3M) systems for the rapid screening of urine specimens for bacteriuria. These systems, which can detect significant levels of microorganisms in urine in five hours (MS-2) or 30 minutes (Lumac), were compared with a standard overnight plate culture method. Three hundred fifty-eight voided urine specimens were examined. The two systems compared equally at greater than 10(5) colony-forming units (CFU)/mL in terms of false-positive results (11%), false-negative results (2%), sensitivity (98%), specificity (approximately equal to 86%), and positive predictive value (98%), although the Lumac was found to have a lower negative predictive value (by 10%) than the MS-2. The only organism not recognized by the MS-2 at greater than 10(5) CFU/mL was a Lactobacillus; whereas the only specimens missed by the Lumac at greater than 10(5) CFU/mL were two pure cultures of Escherichia coli. At counts of greater than 10(4) to 10(5) CFU/mL, both systems missed numerous (15 of 21 isolates for the MS-2; 12 of 9 isolates for the Lumac) gram-positive cocci. The Lumac system was the most costly, being 3.6 times as expensive as the standard plate method. Although both systems greatly reduce the time required to process urine specimens, the large number of false-positive results, false-negative results at greater than 10(4) to 10(5) CFU/mL, as well as cost suggest that a careful evaluation of a laboratory's specific needs for urine cultures be made to determine whether or not such rapid urine screening systems are appropriate.