Evaluation of (SD) MPT64 antigen rapid test, for fast and accurate identification of Mycobacterium tuberculosis complex

Aim: To evaluate the SD MPT64 assay for rapid, preliminary identification of Mycobacterium tuberculosis complex (MTBC). Methods: All specimens were processed using a standard methodology and inoculated into an automated liquid culture system (BD MGIT960). All signal positive cultures had a smear prepared and tested using a commercial molecular assay. From a carefully mixed MGIT960 vial, 100 mu L of broth was loaded into the sample well, and the result recorded after 15 min. Repeat isolates from patients were excluded as were positive cultures contaminated with non-mycobacteria. Results: Fifty MTBC and 150 non-tuberculous mycobacteria were isolated during the study period. Test sensitivity was 98.04%, specificity (98.68%), positive predictive value (96.15%), and a negative predictive value (99.34%). There were two false positive results: Mycobacterium gastri and Mycobacterium fortuitum which were both identified by 16S rDNA and rpoB sequence analysis. Conclusions: The SD MPT64 assay showed excellent performance. The major advantages are: (1) simplicity of test procedure, (2) rapid turnaround time, and (3) relatively inexpensive. When used in conjunction with the presence of serpentine cording in a stained smear from culture, a preliminary identification of MTBC may be made with high confidence.