UN advises ending use of commercial blood tests for tuberculosis

The United Nations World Health Organization (WHO) today recommended ending the use of commercially available blood test kits to detect active tuberculosis (TB), saying that reviews have shown they lead to high rates of misdiagnosis, mistreatment and can potentially harm public health.

The agency instead urged countries to rely on the more accurate microbiological or molecular tests. Tuberculosis kills 1.7 million people every year, and is the major killer of people living with HIV/AIDS.

Testing for active TB through antibodies or antigens found in the blood is extremely difficult, according to the WHO policy recommendation, which says that 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. Different organisms share the same antigens, making tests results unreliable.

“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, 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,” Dr. Raviglione said.

The WHO policy recommendation issued to 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.

The new recommendation comes after 12 months of rigorous analysis of evidence by WHO and global experts.

Some 94 studies were evaluated – 67 for pulmonary tuberculosis (TB in the lungs) and 27 for extrapulmonary tuberculosis (TB in other organs). The results of the studies overwhelmingly showed that blood tests produced an unacceptable level of wrong results – false-positives or false-negatives – relative to other tests endorsed by WHO.

The research revealed “low sensitivity” in commercial blood tests which lead to an unacceptably high number of patients wrongly being given the “all clear” when they in fact have active TB.

The misdiagnosis can result in the transmission of the disease to others or even death from untreated tuberculosis. The studies also revealed “low specificity” with an unacceptably high number of patients being wrongly diagnosed with TB, a factor which could lead to unnecessary treatment, while the real cause of their illness remains undiagnosed and therefore untreated, according to WHO.

The agency said that more than a million of the inaccurate blood tests are carried out annually to diagnose active TB, often at great financial cost to patients.

There are at least 18 of the blood tests available in the market, most of them manufactured in Europe and North America, even though they are not approved by any recognized regulatory body, WHO said.

“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, the Coordinator of TB Diagnostics and Laboratory Strengthening for WHO’s Stop TB department. “It’s a multi-million dollar business centred on selling substandard tests with unreliable results.”