The recent decision by the Ministry of Health and Family Welfare to ban the manufacture, sale, distribution and use of serological (blood) test kits for diagnosing active tuberculosis — both pulmonary and extra-pulmonary — is significant. The blood test diagnoses active TB based on antibody response. The decision does not come as a surprise. In fact, the question was not whether the government would act but how soon it would ban it. In July last year, the World Health Organisation had for the first time issued an “explicit negative policy recommendation” against a practice used in TB care. India’s Revised National Tuberculosis Control Programme also endorsed WHO’s advice. It is unfortunate that the world health body had to step in to put an end to a test that has become widely available in many developing countries despite not being recommended by any regulatory agency. “A blood test for diagnosing active TB disease is bad practice,” the WHO stated in its July communiqué. The reason it came out strongly against the “diagnostic tool” is that the test produces very unreliable results. According to a 2008 WHO report, none of 19 commercially available rapid serological tests studied “performed well enough to replace [sputum] microscopy.” The organisation found that the tests provide “inconsistent and imprecise” results due to their inferior sensitivity and specificity. Unlike in the case of HIV and other diseases, detecting antibody response in people with active TB is difficult and hence unreliable as many factors can cause the response.
According to an August 2011 paper in PLoS Medicine, the blood test, if used in place of sputum microscopy for a year, will be able to diagnose 14,000 more active TB cases but will end up misdiagnosing more than 121,000 people as suffering from the disease (false positive cases). The antibody test is also prohibitively expensive. Every year in India, about 1.5 million serological tests are done at a cost of $15 million. As a result, a staggering number of people end up being wrongly diagnosed and unnecessarily medicated every year. The direct fallout of unnecessary medication is the increased chances of people developing acquired drug resistance, thus further complicating and compromising TB care. But imposing a ban is just the first step towards rooting out the malaise. Since implementing the ban will be a tall order, there is a need for increasing awareness level among the public. Simultaneously, the government should quickly complete the pilot testing of the WHO recommended Xpert MTB/RIF molecular test and make it widely available. Only the availability of a superior alternative can solve the problem.