WHO Warns Against Use of TB Blood Tests

More than a million of these inaccurate blood tests are carried out annually to diagnose active TB, often at great financial cost to patients.

The use of currently available commercial blood (serological) tests to diagnose active tuberculosis (TB) often leads to misdiagnosis, mistreatment, and potential harm to public health, said the World Health Organization (WHO) in a policy recommendation issued recently. 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.

Testing for active TB disease through antibodies or antigens found in the blood is extremely difficult. Patients can have different antibody responses suggesting that they have active TB even when they do not. Antibodies may also develop against other organisms which again could wrongly indicate they have active TB. In addition, different organisms share the same antigens, making tests results unreliable. These factors can result in TB disease not being identified or wrongly diagnosed.

"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," said Mario Raviglione, M.D., director of WHO’s Stop TB Department. "A blood test for diagnosing active TB disease is bad practice. Test results are inconsistent, imprecise, and put patients' lives in danger."

This policy recommendation applies to blood tests for active TB. Blood tests for inactive TB infection (also known as dormant or latent TB) are currently under review by WHO.

This new recommendation comes after 12 months of rigorous analysis of evidence by WHO and global experts. Ninety-four studies were evaluated—67 for pulmonary tuberculosis (TB in the lungs) and 27 for extrapulmonary tuberculosis (TB elsewhere in other organs). Overwhelming evidence showed that the blood tests produced an unacceptable level of wrong results—false-positives or false-negatives—relative to tests endorsed by WHO.

The research revealed "low sensitivity" in commercial blood tests which leads to a high number of patients wrongly being given the “all clear” (a false-negative when in reality they have active TB). This can result in the transmission of the disease to others or even death from untreated tuberculosis. It also revealed "low specificity," which leads to a high number of patients being wrongly diagnosed with TB (a false-positive when in reality they do not have active TB). Those patients may then undergo unnecessary treatment, while the real cause of their illness remains undiagnosed, which may then also result in premature death.

More than a million of these inaccurate blood tests are carried out annually to diagnose active TB, often at great financial cost to patients. Many patients pay up to $30 per test. There are at least 18 of these blood tests available on the market. Most of these tests are manufactured in Europe and North America, even though the blood tests are not approved by any recognized regulatory body.

Cellestis Limited, a biotechnology company in Melbourne, Australia, issued a news release July 25 to clarify that WHO's recommendations don't apply to its QuantiFERON®-TB Gold (QFT) whole blood test, which aids in the diagnosis of both active and latent TB infection. Cellestis said WHO's recommendations refer to serological (antibody-based) blood tests for active TB and not to Interferon-Gamma Release Assays (IGRAs) for diagnosing latent TB, adding that this "has been confirmed by direct correspondence by WHO to Cellestis."

"QuantiFERON-TB was developed in response to the poor quality of previous tests such as those referred by WHO. We thoroughly agree with the comments of WHO regarding serological tests for active TB," said Dr. Jim Rothel, chief scientific officer of Cellestis. "It is imperative to recognize that TB is still one of the world's deadliest diseases. We are confident that QFT has the ability to help reduce the future healthcare burden of TB and potentially help to lower health care costs related to TB and reduce the risk of epidemics.

Tuberculosis kills 1.7 million people every year, and is the major killer of people living with HIV.

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