WHO: Blood tests for tuberculosis are unreliable

The U.N. health agency said it will issue an unprecedented recommendation against using such tests for the infectious lung disease that affects some 14 million people worldwide. As much as a third of the world's population is thought to harbor the bacteria that causes TB.

"The tests are not reliable and a waste of money and time, putting proper care at risk," said Mario Raviglione, the director of WHO's Stop TB department.

A review of the tests has shown that they produce too many false negative and false positive, according to WHO.

Raviglione told The Associated Press that the blood tests "are in fact dangerous to patients, since some cases will not be detected and some will be called TB when in fact they do not have it,"

The WHO guidance will be issued later this week. It is the first time that WHO has issued a "negative" policy, specifically counseling against the use of a particular method for diagnosing a disease.

The use of TB blood tests is particularly common in developing countries such as India, where an estimated 3 million people are infected with the disease.

The Lancet medical journal reported in January that some of the blood testing kits used there are made in developed countries where such tests aren't licensed. They are ordered by doctors who receive greater commissions for the blood tests than for the older and more reliable sputum microscopy method, the journal reported.

"Many of these tests are used in the private-for-profit sector, charging poor people who do not understand the lack of value of the test," Raviglione said.

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