Clinical evaluation of the Abbott RealTime MTB Assay for direct detection of Mycobacterium tuberculosis-complex from respiratory and non-respiratory samples

Abstract Rapid and reliable diagnosis is crucial for correct management of tuberculosis. The Abbott RealTi m e MTB Assay represents a novel qualitative real-time PCR assay for direct detection of M. tuberculosis -complex (MTB) DNA from respiratory samples. The test targets two highly conserved sequences, the multi-copy insertion element IS 6110 and the protein antigen B (PAB) gene of MTB, allowing even the detection of IS 6610 -deficient strains. We evaluated this commercial diagnostic test by analyzing 200 respiratory and, for the first time, 87 non-respiratory clinical specimens from our tertiary care institution and compared its results to our IS 6110 -based in-house real-time PCR for MTB as well as MTB culture. Overall sensitivity for Abbott RealTi me MTB was 100% (19/19) in smear positive and 87.5% (7/8) in smear negative specimens, while the specificity of the assay was 100% (260/260). For both non-respiratory smear positive and smear negative specimens Abbott RealTi me MTB tests showed 100% (8/8) sensitivity and 100% (8/8) specificity. Cycle threshold (Ct) value analysis of 16 MTB positive samples showed a slightly higher Ct value of the Abbott RealTi me MTB test compared to our in-house MTB assay (mean delta Ct = 2.55). In conclusion, the performance of the new Abbott RealTi me MTB Assay was highly similar to culture and in-house MTB PCR. We document successful analysis of 87 non-respiratory samples with the highly automated Abbott RealTi m e MTB test with no inhibition observed.