Evaluation of the MS-2 and Lumac systems for the rapid screening of urine specimens

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.