WHO Says TB Blood Test Inaccurate By Vidushi Sinha | Washington August 10, 2011

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The World Health Organization is urging many low and middle income countries to ban the use of currently-available commercial blood tests to detect active tuberculosis. This is the first time WHO has issued an explicit negative policy recommendation against a practice widely used in tuberculosis care. It is based on two recent studies that found the commonly-used test to be unreliable and misleading -- and even a possible contributor to TB transmission.

 

Tuberculosis kills 1.7 million people a year, around the world. In India, where the blood tests covered by the recommendation are widely used, the government says more than two million new people are infected every year.

In fact, the studies that prompted the WHO action were done in India, where researchers argued the blood tests have contributed to increasing the number of TB infections in the country.

They blamed the inaccuracy of the test for this outcome, saying an undetected, and untreated, case means the infected person can continue to infect others.

Dr. David Dowdy of the Johns Hopkins School of Public Health was a lead researcher in one of the two studies.

“These tests are actively doing people harm by causing them either to take medicines that they don’t need or delaying the diagnosis that they actually do need to get better,” Dowdy said.

Dowdy says that the traditional sputum smear microscopy test is still the cheapest and most effective way of diagnosing TB.
 

But since the sputum test is time-consuming, he says, the blood tests are often preferred because they are simple, straightforward and quicker to run.

Experts also say the blood tests are a multimillion dollar business in developing countries.  The WHO says more than a million of the tests are carried out each year, even though they are not approved by any recognized regulatory body.

“What these tests do is they measure antibodies in the blood against TB so any time anyone has been infected with TB at any time in their life they will develop antibodies against TB.  But the problem is that one person’s antibodies are not going to be the same as the other person. And we don’t have a test yet that can detect antibodies across the board,” Dowdy said.

After the WHO issued its guidelines, the Indian government issued a statement urging doctors and labs not to rely on these imprecise diagnostic tests.

It may take some time, though, before the realities on the ground change in a country as vast as India.

However, experts in the field have welcomed the WHO announcement and the Indian government's response.