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Saturday, June 16, 2007

Tuberculosis blood test no better than standard: review

Blood-based tests to diagnose tuberculosis in developing countries are no more accurate than the older, traditional test, researchers have found.

The standard test for TB, called a sputum-smear test, involves looking for TB bacteria under the microscope in mucus coughed up from the lungs.

But the sputum test is not sensitive, and it is not considered reliable for diagnosing active TB in children or people with HIV.

As an alternative, commercial tests designed to detect antibodies in the blood are being sold to developing countries, where 90 per cent of the world's TB cases occur.

In Tuesday's issue of the Public Library of Science Medicine journal, European and Canadian researchers concluded the blood tests also varied widely in performance, and none were worthy of replacing sputum tests.

"These tests thus have little or no role to play in the diagnosis of pulmonary TB at the present time," the study's authors concluded.

For the study, Madhukar Pai, a professor in McGill's department of epidemiology, biostatics and health, and Richard O'Brien of the Foundation for Innovative New Diagnostics in Geneva reviewed 68 studies on the accuracy of the antibody detection tests.

Although some researchers are trying to improve TB tests for developing countries, drug companies are more interested in targeting other diseases, Pai said. The "dream" test for TB would be a simple, rapid, finger-prick version, he added.

In the meantime, Pai suggested doctors apply the existing tools to detect active cases of TB.

In the developing world, people with tuberculosis may not be able to get a doctor until the disease is at an advanced state, and they may have already spread it to others, the researchers said.

People in developing countries may also be unable to access the continuous drug supply that is needed to prevent the bacteria from gaining resistance to the medications.

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