The World Health Organization has said that blood tests designed to detect active TB are inaccurate and should be banned.

Every year more than two million such tests (mostly in India) are used for TB diagnosis, but the WHO says they are unethical and lead to misdiagnosis and the mistreatment of patients.

In its review of these tuberculosis test kits, WHO found that wrong results in nearly 50% of cases. Most of the 18 kits on the market are produced in Europe and North America, but are mainly sold in developing countries. The WHO says that these blood test kits are prevented from going on sale in Europe and North America due to strict regulations that call for extensive evidence of accuracy. But this is not the case in the developing world - including in India and China, which have weak regulatory mechanisms.

Terming the serological blood test for TB as inaccurate and inconsistent, WHO has recommended that patients in India should opt for sputum microscopy test under DOTS (directly observed treatment, short-course).

But in India, like many other developing countries, TB serological tests (1.5 million) are conducted every year by private doctors and the authorities look the other way in the absence of any guideline to stop the same.

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.

"The evidence we reviewed over the past couple of months shows that one in two patients will be wrongly diagnosed, either false negative or false positive, said Dr Karen Weyer, also from the WHO Stop TB department.

"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."

"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 of these inaccurate tests."

The new recommendation from the WHO comes after 12 months of evaluating ninety-four studies — 67 for pulmonary tuberculosis (TB in the lungs) and 27 for extra pulmonary tuberculosis (TB elsewhere in other organs). Overwhelming evidence showed that the blood tests produced an unacceptable level of wrong results — false-positives or false-negatives — relative to tests endorsed by WHO.

The health experts in India say the public need to have faith on the treatment being provided under the RNTCP which is free of cost and within the approved WHO guidelines.

But they say diagnostic delays are all too common and by the time a patient is diagnosed with TB, he/she has already visited multiple doctors and infected several others, perpetuating the cycle of TB transmission.

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