Tuberculosis (TB) kills 1.7 million people every year, and this antiquated disease remains the major killer of people living with HIV. Improving the early and effective diagnosis of TB is a priority action for WHO and the international TB community. TB research is currently underway to bring better and more rapid tests that are easy to administer, effective and accurate.
Testing for active TB disease through antibodies or antigens in the blood is extremely complicated. Antibodies may also develop against other organisms which could lead to false positive result for active TB. Moreover, different organisms share the same antigens, making tests results unreliable and these factors might lead to TB disease not being identified or wrongly diagnosed.
According to Dr Mario Raviglione, Director of WHO Stop TB Department, “WHO is calling for an end to the use of these serological tests to diagnose tuberculosis in the best interests of patients and caregivers in the private and public health sectors”. He also added that, “A blood test for diagnosing active TB disease is bad practice and these test results are inconsistent, imprecise and put patients' lives in danger."
The new recommendation comes as a result of 12 months of rigorous analysis of evidence by WHO and global experts. Ninety-four studies were evaluated - 67 for pulmonary TB and 27 for extrapulmonary TB. The blood tests were observed to give an unacceptable level of wrong results - false-positives or false-negatives – when compared to tests endorsed by WHO.
The research revealed "low sensitivity" in commercial blood tests which leads to an unacceptably high number of patients given false-negative results when in reality they have active TB, which could result in the transmission of the disease to others in the community. It also revealed "low specificity", which leads to an unacceptably high number of patients being wrongly diagnosed with TB (false positive) when in reality they do not have active TB. Moreover, these inaccurate blood tests are expensive and patients have to pay up to US$30 per test.
Thus, 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.
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