The World Health Organization is urging health officials to ban
commonly-available blood tests for tuberculosis. W.H.O. officials
made the call after two studies found that results from a commonly
used test are undependable and misleading.
The blood tests are low-cost and produce fast results. They are
widely used in developing countries, especially India. The Indian
government says the country has more than two million new cases of
TB a year.
But, researchers say the tests being sold are dangerously
inaccurate. They say the results are wrong in fifty percent of
David Dowdy studies infectious diseases at the Johns Hopkins
Bloomberg School of Public Health in Baltimore, Maryland. He led
one of the studies.
DAVID DOWDY: "These tests are actively doing people harm by
causing them either to take medicines that they don't need or
delaying the diagnosis that they actually do need, to get
Traditional tests for TB examine the sputum, a material found in
a person's lungs. Active TB is identified if certain bacterium
grows in the test material. However, these tests take longer to
carry out. Dr. Dowdy says the blood tests are widely used because
of the speed of results.
DAVID DOWDY: "What these tests do is they measure antibodies in
the blood against TB so anytime anyone has been infected with TB at
any time in their life, they will develop antibodies. The problem
is that one person's antibodies are not going to be the same as
another person's antibodies. And we don't have a test yet that can
detect these antibodies across the board."
The leader of the other study was Madhukar Pai, an
epidemiologist at McGill University in Montreal, Canada. He says
the tests are usually used by private medical centers -- not
government TB control programs.
MADHUKAR PAI: "So these tests are uniformly not used in the
developed world. They are mostly used in countries with weak
regulation, and lack of regulation allows these sorts of tests to
be on the market and used freely."
Experts say the blood tests are a big business in developing
countries, worth millions of dollars a year. The World Health
Organization says a million of the tests are done every year. But,
the tests are not approved by any recognized supervisory group.