Comparison of the ligase chain reaction with solid and liquid culture media for routine detection of Mycobacterium tuberculosis in nonrespiratory specimens

The aim of this study was to compare the results of a commercial assay base d on the ligase chain reaction [(LCR) LCx Probe System MTB; Abbott, USA] wi th those of culture in liquid medium (Septi-Chek AFB; Becton-Dickinson, USA ) and culture on the egg-based Lowenstein-Jensen solid medium for the direc t detection of Mycobacterium tuberculosis complex in nonrespiratory specime ns. The results were analyzed according to the standard definition of a tru e-positive result. Two hundred thirty-five nonrespiratory samples routinely submitted to rule out tuberculosis were analyzed. All samples were smear-n egative. Mycobacterial growth in either culture medium was detected in 18 ( 7.6%) specimens: Mycobacterium tuberculosis was recovered from seven (38.9% ) specimens cultured on Lowenstein-Jensen medium and from 18 (100%) specime ns cultured in Septi-Chek AFB. The LCR protocol was positive in 22 specimen s. None of the LCR-negative controls showed positive results. All samples p ositive by culture on Lowenstein-Jensen medium were positive by culture in liquid medium and by the LCR assay. However, Mycobacterium tuberculosis was detected by culture in liquid medium in two specimens that were negative b y the LCR assay, whereas six specimens negative by culture in liquid medium were positive by the LCR protocol; three of these were identified as true- positive results of the LCR assay. The sensitivity, specificity, and positi ve and negative predictive values were 33.3%, 100%, 100%, and 93.8%, respec tively, for Lowenstein-Jensen medium; 85.7%, 100%, 100%, and 98.6% for the liquid medium; and 90.4%, 98.5%, 86.3%, and 99% for the LCR assay. These f indings indicate that the LCR assay may be a valid method of high diagnosti c yield for direct detection of Mycobacterium tuberculosis complex in nonre spiratory specimens.