Some patients may have antibody responses to tests that seek out antibodies or antigens which suggest they have TB, when in fact they don't. Antibodies which have responded to other (non-TB) organisms may cause doctors to diagnose TB incorrectly. In other cases, those with TB may not be diagnosed through tests that seek out antibodies.
Dr Mario Raviglione, Director of WHO Stop TB Department, said:
"In the best interests of patients and caregivers in the private and public health sectors, WHO is calling for an end to the use of these serological tests to diagnose tuberculosis. A blood test for diagnosing active TB disease is bad practice. Test results are inconsistent, imprecise and put patients' lives in danger."
WHO stresses that this policy recommendation refers to blood tests for active TB only, not inactive (dormant, latent) TB, which is currently being reviewed.
WHO informs that its new recommendations are the result of 12 months of thorough evidence of data analyzed and discussed by WHO and experts from around the world, who evaluated 94 studies - 27 for extrapulmonary TB and 67 for pulmonary TB. The evidence is compelling that blood tests are too unreliable, resulting in false-positives or false-negatives, compared to those that WHO endorses.
A significant number of commercial blood tests lead to too many patients being given the 'all clear' incorrectly - false-negatives. They are infected, thinking they are not, and transmit the disease to others. Left untreated, TB can be fatal. Other commercial tests may do the opposite, uninfected patients are wrongly diagnosed and undergo unnecessary treatment. Some of these patients may have some other illness which goes untreated.
Waste of resources - over one million inaccurate tests are performed each year to diagnose active TB. In many cases the patient has to pay $30 for a test. Tragically, these tests (18 different ones) are manufactured in North America and Europe where their own regulatory authorities have not approved them.
Dr Karin Weyer, Coordinator of TB Diagnostics and Laboratory Strengthening for the WHO Stop TB Department, said:
"Blood tests for TB are often targeted at countries with weak regulatory mechanisms for diagnostics, where questionable marketing incentives can override the welfare of patients. It's a multi-million dollar business centred on selling substandard tests with unreliable results."
1.7 million people die from TB worldwide annually. TB is a key killer of patients with HIV.
Tuberculosis, also known as TB is a highly infectious disease caused by Mycobacterium tuberculosis, a bacterium. It mainly affects the lungs, but can also affect the circulatory system, lymphatic system, and CNS (central nervous system). It used to be called consumption because the disease would consume anyone who became infected from within.
Most infected people have no symptoms. When they do appear, they may include tiredness, shortness of breath, chills, nights sweats, unexplained weight loss, and loss of appetite. The cough will last several weeks (coughing may be painful), the patient may cough up blood, have chest pains, and painful breathing.
Written by Christian Nordqvist