Blood test to detect TB is inaccurate and not cost effective

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The current blood sample test used to detect active TB is not accurate or cost effective, according to new findings.

There are two forms of TB; active TB where people experience symptoms and are infectious, and latent TB where people are infected with the TB bacteria but have no symptoms and are not able to spread the bacteria.

Blood tests for active TB are widely available for sale in low and middle income countries, but these latest findings have formed the basis of a new policy issued by the World Health Organisation (WHO), urging countries to ban the unapproved blood tests and instead rely on other forms of testing.

Two new studies evaluated the blood test. In the first study, the researchers evaluated previous research papers looking at the accuracy of commercial blood tests. In their review, the researchers found many cases where the blood test showed as positive when the patient did not have TB, and negative when the patient did have confirmed TB. Overall, they concluded that the quality of evidence was very low.

In the second study, the authors analysed the cost-effectiveness of a TB blood test, compared to other forms of diagnosis. Their results showed that if the blood test was used as the first test for TB, it would result in more premature deaths, more secondary infections and more inaccurate diagnoses, which increase the cost of treatment.

The WHO report urges the use of alternative testing methods and strongly encourages further targeted research to identify new tests for TB diagnosis and alternative blood tests which would need to have much improved accuracy.

Today's recommendation does not apply to blood tests for latent TB infection, which are currently under review by the WHO and the findings are expected to be released next month.


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