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WHO Recommends End to Serological Tests for TB, Urges MDx Testing

By a GenomeWeb staff reporter

NEW YORK (GenomeWeb News) – The World Health Organization this week called for ending the use of commonly available blood tests for active tuberculosis, saying the results from them are inaccurate and often are targeted at countries "with weak regulatory mechanisms."

The tests being targeted by WHO are antibody-based and the organization cites a number of difficulties surrounding their performance, such as different antibody responses by different patients, which may result in incorrect diagnoses of active TB. Also, antibodies may develop against other organisms, and different organisms may share the same antibodies, making such tests unreliable.

"WHO is urging countries to ban the inaccurate and unapproved blood tests and instead rely on accurate microbiological or molecular tests, as recommended by WHO," it said in a statement.

The organization previously endorsed the use of Cepheid's Xpert MTB/RIF test, which WHO characterized at as a "major milestone for global TB diagnosis and care."

"In the best interests of patients and caregivers in the private and public health sectors, WHO is calling for an end to the use of these serological tests to diagnose tuberculosis," Mario Raviglione, director of the WHO Stop TB Department, said in the statement this week. "A blood test for diagnosing active TB disease is bad practice. Test results are inconsistent, imprecise, and put patients' lives in danger."

The recommendation from WHO applies to the diagnosis of active TB. Antibody-based tests for inactive TB — also known as dormant or latent TB — remain under review by WHO.

In reaching its policy recommendation, WHO and global experts analyzed 94 studies during the past 12 months — 67 for pulmonary TB and 27 for extrapulmonary TB. According to WHO, the "overwhelming" evidence suggests that blood, or serologic, tests produce an "unacceptable level" of false positive or false negatives, relative to tests endorsed by WHO.

In addition to expressing concerns about the sensitivity and specificity of the blood tests, WHO said that quality standards for the tests are being sacrificed for commercial interests. At least 18 such tests are currently available with more than 1 million test procedures carried out each year.

Most of the tests are manufactured in Europe and North America, although they are not approved by any recognized regulatory body.

"Blood tests for TB are often targeted at countries with weak regulatory mechanisms for diagnostics, where questionable marketing incentives can override the welfare of patients," said Karin Weyer, coordinator of TB Diagnostics and Laboratory Strengthening for the WHO STOP TB Department. "It's a multi-million dollar business centered on selling substandard tests with unreliable results."

WHO said that the explicit negative policy recommendation is its first against a practice that is widely used in TB care, and underscores its "determination to translate strong evidence into clear advice to governments."