A study conducted by the doctors at All India Institute of Medical Sciences (AIIMS) recently, proved that the gene expert test otherwise known as Xpert MTB/RIF or CBN test — used to diagnose multidrug resistant TB — gives inaccurate results. According to the study, approximately 35 per cent patient samples gave erroneous results. This study was published in the online edition of America’s Medical Journal (Journal of Clinical Microbiology). The doctors at AIIMS have claimed that tests like MGIT liquid culture and molecular test lPA are more efficient in countries like India.
“In 2012-13 samples of over 405 patients were collected and a comparative study of MGIT liquid culture, lPA and gene expert was done on them. It was observed that the accuracy of liquid culture and lPA test was 100 per cent whereas an inaccuracy of 35 per cent was observed in the outcome obtained from gene expert tests,” said Dr Sarman Singh, head of Clinical Microbiology and Molecular Medicine at AIIMS.
As per WHO guidelines, four tests are approved for this procedure - lED microscope, liquid culture and two molecular tests which are gene expert and line probe assay. Gene expert is one of the most advanced tests for TB diagnosis where the test report gets generated in merely two to three hours. It also indicates whether the ongoing first line medicine will work for the patient or not. The test is available at AIIMS for patients suffering from drug resistance TB. As the test is costly, it is not available in all the hospitals, but central TB division of Ministry of Health is installing gene expert in all the referral TB laboratories.
While the study does point out the inaccuracy of the test, it also states that the test gave accurate results in South Africa. “The scientists at AIIMS found that Indian strains have a peculiar gene sequence which is not recognized by the probes Gene expert has. Hence, if such systems are used routinely, this would give a false impression that India has very low Rifampicin resistance thus making the programme mangers complacent. Government of India should generate its own data regarding efficacy of various diagnostic tests to improve performance in detecting the drug resistance,” added Dr Singh. AIIMS doctors also stated that in case of multidrug resistance, TB liquid culture test is more reliable. Thus, it has also been made affordable now. The test is now available for Rs 900 in WHO registered private laboratories in Delhi.