GENEVA - The World Health Organisation (WHO) called on Wednesday for an immediate halt to the use of blood tests to detect active tuberculosis, saying they were faulty and leave millions of people at risk.

Production of the test kits, WHO officials said, was largely by Western companies which export them to developing countries because they have not passed regulatory standards in rich nations.

"Overwhelming evidence showed that the blood tests produced an unacceptable level of wrong results" which led to misdiagnosis and mistreatment, the United Nations agency said after a year-long analysis.

Studies showed that at least half the tests find the disease in patients when it is absent or give the all-clear when TB is present. "So they put patients lives in danger," said WHO TB prevention chief Mario Raviglione.

At least two million of the tests are carried out each year in some 17 poorer nations -- including China and India -- almost exclusively by doctors and health workers in the private or semi-private sector, according to the WHO.

"The WHO is urging countries to ban the inaccurate and unproved blood tests and instead rely on accurate microbiological or molecular tests, as recommended by the WHO," a statement from the agency said.

WHO TB specialist Karin Weyer told a news conference to announce the highly unusual move by the agency that it had been asked by the government of India to launch a detailed analysis of the tests -- on sale since the mid-1990s.

The WHO had never recommended their use. The tests "are often targeted at countries with weak regulatory mechanisms for diagnostics, where questionable marketing incentives can override the interests of patients", Weyer said.

"It is a multi-million dollar business centred on selling sub-standard tests with unreliable results."

Most of the tests were manufactured in Europe and North America -- including France, Italy, Germany, the Netherlands and the United States -- "even though the blood tests are not approved by any regulatory body", the WHO statement said.

The WHO warning, which has been passed on to several governments, is the first time it has issued an explicit "negative" policy recommendation against a practice that is used in the care of TB -- which kills 1.7 million people a year.

The tests, of which there are at least 18 available on the market, "must be stopped immediately and everywhere", Raviglione told the news conference.