Updated on 20 February 2013
Serological tests for TB - Boon or bane
The recent ban on serological diagnostic test by the government of India has cast a shadow on the rampant rise in the popularity of these tests. Although agreeing with other experts on the banning aspect, Professor Singh differs slightly on an important aspect. "I am still not sure whether the kits are being imported. Perhaps, some kits of old stock are still available with some firms," said Professor Singh.
Dr Navin Dang, director, Dr Dang's Laboratory, said, "We must not look for the so called market potential of such kits. It is a fact that these kits were earlier being used by all the labs but after the ban, all the responsible companies have discontinued the use. However, these kits are imported and used illegally. Hence, we must not encourage this market by any means whatsoever."
Since July 2012, one of the major diagnostic lab networks in India, SRL Diagnostics has stopped offering TB serology assays at all its lab locations. Many people like Dr Madhukar Pai, associate professor, McGill University, Canada, believe that, although many large labs have stopped using TB serology, the small ones are still continuing to use them, especially the rapid (lateral flow) test versions. When questioned, few of the small time labs pointed out that such tests are available in almost 80 percent of the labs, mostly in remote areas. However, fearing the legal implications, no one was ready to say anything publicly about the mechanisms of importing and distribution.
Dr Pai feels that there is no valid, accurate test for TB using blood as the sample. He says, "Nowhere in the world is active TB diagnosed using blood specimens. So, from that perspective, there is no real alternative. There is a FDA approved, acceptable blood test for latent TB infection (not active TB), which is called as QuantiFERON TB Gold (marketed in India as TB Gold). Some big labs have started replacing antibody serology tests with this TB Gold, but that is a big problem. TB Gold cannot separate latent infection from active TB and therefore will show positive results for a large number of Indians."
Alternatives to serological tests
Experts say that, if doctors and labs are willing to use sputum (not blood), then there are some really good alternatives. Sputum smear microscopy is the standard test used in many countries. In addition, there is liquid culture which can produce highly accurate results within 10 days. More recently, WHO has approved the GeneXpert test (Cepheid, California) and this test is being scaled up in over 20 countries. It is much more accurate than sputum smears and can produce results within 90 minutes.