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 5 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 >10⁵ colony-forming units (CFU)/mL in terms of false-positive results (11%), false-negative results (2%), sensitivity (98%), specificity (≃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 >10⁵ CFU/mL was a Lactobacillus; whereas the only specimens missed by the Lumac at >10⁵ CFU/mL were 2 pure cultures of Escherichia coli. At counts of >10⁴ to 10⁵ CFU/mL, both systems missed numerous (15 of 21 isolates for the MS-2; 12 of 19 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 >10⁴ to 10⁵ 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.