[Clinical utility of a commercial ligase chain-reaction kit for the diagnosis of pulmonary and extrapulmonary tuberculosis in the adult].

Microscopy with the Ziehl-Neelsen (ZN) stain is frequently negative in paucibacillary tuberculosis (TB) so that the treatment must be started and continued until the culture results confirm or not the disease. LCx Mycobacterium tuberculosis Assay (Abbott, Lab.) uses the ligase chain reaction for direct amplification of DNA and rapid detection of M. tuberculosis Complex (MTB) in clinical specimens. We evaluated the usefulness of the LCx assay on 1,203 clinical samples: 737 respiratory and 466 extrapulmonary specimens. The LCx results were compared with those obtained by ZN and cultures on solid media and Mycobacteria Growth Indicator Tube (MGIT, Becton Dickinson, Argentina). Since detection and identification of MTB are simultaneously made by the LCx assay, a total of 145 out of 183 patients (79.2%) had a confirmed TB diagnosis in two working days. Positive culture results were predicted in 122 out of 160 cases (76.3%) by LCx and in 70 (43.8%) by ZN as well. The sensitivity (S) and specificity (ES) of LCx assay in ZN positive cases were 93.4% and 100.0% while in ZN negative cases they were 68.0% and 98.6%. The overall S and ES were 79.2% and 98.7%, respectively. We conclude that the LCx assay is a rapid and sensitive technique, which can be a helpful diagnostic tool mainly for paucibacillary TB in reference laboratories.