Blood tests designed to detect active TB are inaccurate and should be banned, the World Health Organization has said.

More than two million such tests are carried out annually, but the WHO says they are unethical and lead to misdiagnosis and the mistreatment of patients.

The organisation’s review of these tuberculosis test kits says they give wrong results in around 50% of cases.

The kits are mainly sold in the developing world.

However, most of the 18 kits on the market are produced in Europe and North America.

According to Dr Mario Raviglone, the director of the WHO Stop TB Department, the tests must be banned.

He said: “A blood test for diagnosing active TB disease is bad practice. Tests are inconsistent, imprecise and put patients’ lives in danger.”

The tests work by detecting antibodies or antigens in the blood that are produced in response to the bacterium.

But some of these commercial tests have what’s called “low sensitivity” which leads to large numbers of patients being told they do not have TB when they do.

Dr Karen Weyer, who is also from the WHO Stop TB department, added: “The evidence we reviewed over the past couple of months shows that one in two patients will be wrongly diagnosed, either [as] false negative or false positive.

“If it’s a false negative patients get the all clear when they in fact have TB, the disease continues to spread, and the patients may die.

“If, on the other hand, it’s false positive, patients are put on treatments unnecessarily while the true cause of their disease remains undiagnosed.”

“We would describe this as unethical – and we are making a very strong urge to governments to consider that TB is a threat and the use of these ineffective tests is also a threat.”

The WHO says that the tests which are manufactured in Europe and North America are prevented from going on sale where they are made due to regulations that call for extensive evidence of accuracy.

But this is not the case in the developing world – including in India and China.

Dr Weyer added: “One of the major problems is that these developing countries often have little or very weak regulatory mechanisms to make sure that tests are registered before they are used at country level.

“Another problem is that these tests are often used in the private sector, which is a difficult sector to regulate and as a result there is a wide misuse, I would say, of these inaccurate tests in the private sector in at least 17 countries that we are aware of.”

She said there was a need for a TB test that could be used “at the bedside”. But she added: “We don’t have a blood test for TB that can be used at the point of care level.”

The WHO says this call for a ban is a highly unusual move – It’s the first time the organisation has issued an explicitly negative policy recommendation against a practice that is widely used in tuberculosis care.

TB kills 1.7m people every year, and is the biggest cause of death of people living with HIV.