Rapid Tuberculosis Detection Test Endorsed by Experts

A diagnostic test for tuberculosis (TB) that can accurately and quickly detect both TB and drug-resistant strains has been authorized by leading experts in the field.

The diagnostic accuracy of the Xpert MTB/RIF test can provide timely advice for clinicians and policymakers in countries where TB is a major public health problem and where drug resistance further complicates efforts to control TB.

Scientists from the Cochrane Infectious Diseases Group, McGill University (Montreal, QC, Canada) and the Foundation for Innovative New Diagnostics (FIND; Geneva, Switzerland), analyzed data from 18 studies involving a total of 7,816 people, with most studies being carried out in low- and middle-income countries. Their analysis showed that when Xpert MTB/RIF test is being used as a replacement for smear microscopy for 1,000 people being screened, of whom 150 have TB, the test picks up 132 of the 150 cases (88%) and falsely diagnoses 17 (2%) with TB.

Where the Xpert test is being used as a replacement for culture-based drug susceptibility testing, it is also able to detect the equivalent of 141 out of 150 cases (94%) of rifampicin resistance. When Xpert is used as a follow-on test, after conventional smear microscopy has already produced a negative result, it picks up 101 out of 150 cases (67%). As smear-negative TB is not picked up by smear microscopy because microscopy cannot detect small numbers of bacteria, Xpert picked up 67% of this group that would have been missed by microscopy.

The authors concluded that when the Xpert assay is used as an initial diagnostic test for TB detection and rifampicin resistance detection in patients suspected of having TB, multi-drug-resistant (MDR)-TB, or human immunodeficiency virus (HIV)-associated TB, it is both sensitive and specific. Xpert may also be valuable as an add-on test following microscopy for patients who have previously been found to be smear-negative. An Xpert result that is positive for rifampicin resistance should be carefully interpreted and take into consideration the risk of MDR-TB in a given patient and the expected prevalence of MDR-TB in a given setting. The Xpert MTB/RIF test is manufactured by Cepheid Inc (Sunnyvale, CA, USA).

Karin Weyer, DSc, Coordinator, Laboratories, Diagnostics and Drug Resistance at the World Health Organization (WHO; Geneva, Switzerland) said, "This Cochrane Review provides high quality evidence that reinforces WHO's endorsement of this test. Recent price reductions have greatly facilitated rollout of this technology with 1.4 million test cartridges and over 200 GeneXpert instruments for the rapid detection of TB and rifampicin resistance will be distributed in 21 countries with a high burden of TB." The review was published on January 31, 2013, in the Cochrane Library.

Related Links:
McGill University
Foundation for Innovative New Diagnostics
Cepheid Inc.