Comparative Evaluation of the New Gen-Probe Mycobacterium tuberculosis Amplified Direct Test and the Semiautomated Abbott LCx Mycobacterium tuberculosis Assay for Direct Detection of Mycobacterium tuberculosis Complex in Respiratory and Extrapulmonary Specimens

Abstract

Two commercial assays that detect Mycobacterium tuberculosis complex (MTB) in clinical specimens by rRNA target amplification (AMTDII) and ligase chain reaction (LCx) were evaluated. The tests were applied to 457 respiratory (n = 273) and extrapulmonary (n = 184) specimens collected from 357 patients. The results were compared with those of acid-fast staining and culture. The combination of culture and clinical diagnosis was considered to be the “gold standard.” Seventy specimens were from patients with pulmonary tuberculosis and 28 specimens were from patients with extrapulmonary tuberculosis. After resolution of discrepant results, the overall sensitivities, specificities, and positive and negative predictive values for respiratory specimens were 92.8, 99.4, 98.5, and 97%, respectively, for AMTDII and 75.7, 98.8, 96.4, and 90.5%, respectively, for LCx. With extrapulmonary specimens, the overall sensitivities, specificities, and positive and negative predictive values were 78.6, 99.3, 95.6, and 96.2%, respectively, for AMTDII and 53.6, 99.3, 93.7, and 92.1%, respectively, for LCx. The level of agreement between AMTDII and LCx assay results was 78.2%. We conclude that although both nucleic acid amplification methods are rapid and specific for the detection of MTB in clinical specimens, AMTDII is significantly more sensitive than LCx with both respiratory (P = 0.005) and extrapulmonary (P = 0.048) specimens.

Multicenter Evaluation of the Abbott LCx Mycobacterium tuberculosis Ligase Chain Reaction Assay

“…After resolution of discrepant results, the sensitivity, specificity, PPV, and NPV for respiratory specimens were 70.2, 99.9, 98.9, and 98.0%, respectively. These findings agree with previous evaluations of the LCx assay, which reported values of 77.1 to 90.2, 98.4 to 100, 72.8 to 100%, and 90.5 to 99.5%, respectively (3,20,24,28,31,36,39,45). The assay sensitivities for smear-positive and smear-negative respiratory specimens were 98.5 and 41.5%, respectively (Table 3).…”

“…For resolved data, the sensitivities for smear-positive and smearnegative pulmonary specimens were 93 to 100 and 43 to 81%, respectively, for the Gen-Probe amplified Mycobacterium tuberculosis direct test (8,9,14,26,30,41,42), 89 to 97.6 and 42.9 to 74%, respectively, for the Roche Mycobacterium tuberculosis Amplicor test (6,7,10,14,15,27), and 90 to 96 and 48 to 68%, respectively, for the Cobas Amplicor test (32,34). Although the LCx assay is not licensed for use with nonrespiratory specimens, the sensitivities were 84.6 and 57.1% for smear-positive and smear-negative specimens, respectively, in the present evaluation; these findings were comparable to those of other studies investigating the performance of the LCx assay with nonrespiratory specimens (81.8 to 100 and 35.3 to 71.1%, respectively (18,31).…”

“…The present study has attempted to avoid these biases. Consecutive samples submitted to the participating laboratories were tested; the sample cohort was not enriched with positive samples; hence, the prevalence of culturepositive samples was relatively low (i.e., 6.5%) and the sensitivity of the present study is among the lower of published estimates (3,20,24,28,31,36,39,45). Furthermore, an average of only 1.6 specimens were collected per patient, and the 152 culture-positive specimens were collected from 98 patients (for 94% of these patients three or fewer samples were collected, with an average of 1.5 specimens collected from each patient).…”

“…The gene is specific for members of the MTBC (38). The LCx assay was designed for use with processed respiratory specimens, although two studies have evaluated the assay with nonrespiratory specimens (18,31). The aims of the present study were to evaluate the performance of the LCx assay with respiratory and nonrespiratory specimens and to review the setting of the sample rate/ cutoff value, presently set at a value of 1.0, to determine whether the cutoff value may be reduced to improve test sensitivity without unduly compromising specificity.…”

Rapid and Sensitive Detection Method of a Bacterium by Using a GFP Reporter Phage

“…This method has some drawbacks: Its sensitivity is insufficient; bacteria must be purified from biological samples; and the process takes many hours. Polymerase chain reaction (PCR) has recently been used to detect bacteria and viruses (4,5,13). This method provides improved sensitivity, but it too is laborious as well as expensive.…”