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Experts question new TB test,say could lead to drug resistance

US to spot latent infection,in which a carrier does not spread the disease but can proliferate the bacteria.

Written by Abantika Ghosh | New Delhi |
April 15, 2013 1:20:49 am

Efforts to promote a tuberculosis test,recommended in the US,as a diagnostic test by laboratories in India is facing stiff resistance by medical experts who are questioning its efficacy.

The test,Interferon Gamma Release Assay (IGRA),is used in the US to spot latent infection,in which a carrier does not spread the disease but in favourable conditions can proliferate the bacteria. The IGRA test is a whole blood TB test that checks not the presence of TB bacteria but the immune response of the body to the bacteria. Medical experts say the test could give rise to possible drug resistance,something that led to the ban of serological test for TB diagnosis.

The training module for community pharmacists brought out by the Revised National TB Control Programme (RNTCP) in January says,“There is no role for IGRA test in clinical practice for the diagnosis of TB.” But the labs argue that it is the only test available for TB cases where organs other than lungs are infected.

Doctors says it is not a reliable diagnostic test as a person with latent infection would give a positive result though the person may not actually be a TB case. This situation might lead to the danger of administering TB antibiotics to a person who does not need it. It exposes the organism to a curtailed dose of the drug,thereby creating resistance.

Ashok Kumar,Deputy Director General of Central TB Division,says the test cannot be banned as it is not marketed as a diagnostic test. “Starting a person on TB drugs based on IGRA can lead to resistance,” he said.

The test is mandatory to get US visa for some jobs. “It is not a confirmatory test for TB. But we do it when doctors ask for it. If there are clinical doubts of TB in organs other than lungs,doctors may want to be sure that there is no TB,” said Dr Rakesh Sharma of North Delhi Pathology Clinic. But Dr S Chatterjee,consultant,internal medicine,Indraprastha Apollo Hospital,said neither positive nor the negative result from this test is reliable.

Diagnostic labs are dismissive of RNTCP recommendation. “It is not a banned test and we do it regardless of what the government says. The government made those recommendations as they were trying to promote the molecular test at the instance of a big international donor organisation. Go to CDC Atlanta website and check how important the test is,” said Dr Pradeep Suri of Dr Suri’s Pathlabs. Experts question the logic of this test in India. “To tackle latent TB infection,one would need to prescribe nine months of anti-TB drugs which the person may or may not complete. You risk side-effects and resistance,” said Dr Manish Kakkar of the Public Health Foundation of India.

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