Now, African study says hi-tech TB test gives inaccurate results

Days after a study by the All India Institute of Medical Sciences (AIIMS) raised questions on the accuracy of the Gene Xpert test, conducted to find out a drug resistant form of tuberculosis in two hours, another African study published in the latest international medical journal reveals discrepancy in the results.

The procedure was seen as a major breakthrough in tuberculosis management. Mumbai presently has six Gene Xxpert machines in public healthcare and more than six in private sector.

Dr Yatin Dholakia, secretary of Maharashtra state anti-TB association said: "GeneXpert is a PCR based test and thus the possibility of detecting dead bacilli in patients previously treated and having chest symptoms is always there. This was proved in the study."

Dr Dholakia further added that care should be therefore taken by the health authorities and not rely completely on the test. "GeneXpert should be used as a screening test only which should be crossed checked with the regular sputum culture test," added Dr Dholakia.

Dr Samsuddin Khan, state TB project coordinator (Maharashtra and Goa), also expressed similar views.

However, the Brihanmumbai Municipal Corporation's health department is not worried with the AIIMS study. Dr Mini Khetrapal, Mumbai tuberculosis officer said: "In Mumbai, we only subject tuberculosis patients who we suspect are multi-drug resistant TB patient. New tuberculosis suspect patients are not sent for Gene Xpert. Therefore there is no point of missing patients."

There are four tests approved by WHO: LED Microscope, Liquid Culture and two molecular tests - Gene Xpert and Line Probe Assay. The centre is in the process of installing Gene Xpert machines in all referral TB laboratories.

What is PCR?
Sputum sample of the patient is fed to the machine and with the biochemical reactions, it detects whether the sample contains the TB bacterium. The machine looks for the DNA specific to the TB bacterium. If there are TB bacteria in the sample, the machine will detect their DNA and automatically multiply it. This technique is called PCR (polymerase chain reaction), and allows the machine to also look at the structure of the genes.