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Blood test to detect TB is unreliable: WHO

health-and-fitness Updated: Aug 08, 2011 23:54 IST
Chetan Chauhan
Chetan Chauhan
Hindustan Times
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The World Health Organisation (WHO) has termed the commonly used methodology to detect tuberculosis (TB) as unreliable with Indian health ministry deciding to issue an advisory to hospitals to discontinue popular blood tests.

The blood tests are conducted on about two million people every year to detect tuberculosis, of which the WHO says about half of the results are wrong. Both private and government hospitals in India use blood tests to detect TB.

"They are a waste of time, and they are a waste of money, and very importantly, they put at risk those people who suffer from TB," Mario Raviglione, director of WHO's Stop TB department said, while releasing a negative policy recommendation for the tests.

This comes after the WHO started investigating the blood tests in 2005 after governments reported increase in prevalence of TB despite machinery to provide medical aid to the patients.

“The tests may have failed to detect TB and by the time it got detected it was too late,” said a senior health ministry official.

After a six year long analysis, the WHO termed the tests as a money making business centered on selling substandard tests on unreliable results. The WHO also found that some companies had remarketed the tests under different names after the earlier versions were found to be giving imperfect results.

The doctors were also getting financial incentives to conduct the test based on detection of antigens produced by Mycobacterium tuberculosis, the organism that causes TB.

The WHO also warned that consequences of such inaccurate diagnoses were significant as TB goes untreated and individuals are not only at risk of death but also unknowingly transmit the disease to others.

“Antibody response is a poor indicator because the various types of mycobacteria share antigens, and other infections raise similar antibody responses,” said a report published in Science Magazine this week.

In place of blood tests, the WHO has recommended use of standard microscopy or a new molecular testing system called GeneXpert.

“The advantage of GeneXpert is that you can immediately diagnose TB and determine whether that TB is drug resistant or not,” the WHO said.

The new test provides results in two hours compared with the weeks required to complete a traditional TB culture diagnosis. However, the testing equipment costs US $ 20,000.

Although Health ministry has not suggested any alternative it wants medical associations across India to look for affordable alternatives in wake of the WHO finds.