Tuberculosis
A recent study in the Lancet Infectious Diseases Journal states that the rapid blood tests which are currently used in diagnosis may not be accurate enough.
Image for representation.

Tuberculosis has long been a problem which has plagued the nation. The World Health Organisation (WHO) estimated that around 2.79 million cases of TB were detected in India in 2016 alone. A recent study published in the Lancet Journal of Infectious Diseases questions whether the most commonly used methods of testing for TB are effective enough to diagnose the issue on such a large scale. Experts in India, however, seem divided on this.

Dr Anil Kumar, deputy director of TB Control and Eradication Program in Karnataka said, “The methods that we use to diagnose tuberculosis in India are those which have been tested and tried. These are the diagnostic tools recommended by the WHO. From sputum smear microscopy to a nucleic acid-based genetic application test, we use very effective methods to identify those who are tuberculosis positive,” he stated.

“Whatever tests are approved and endorsed by the WHO are used and available throughout the country. Irrespective of someone’s socioeconomic background, these are the standard diagnostic measures used," he explained.

However, not all experts seem to agree. Dr Roshan Santhosham, a Chennai-based pulmonologist, states that while the sputum smear is effective in detecting late cases, it’s not necessarily enough to pick up an early case of TB.

“Staining is no longer considered the 'true' gold standard test. The geneXpert is the test which should be used for that because it is more accurate. Take any specimen, whether sputum or a tissue sample, place it in the cartridge, and the machine amplifies the genome of the bacteria. Even very low samples of the virus can be picked up in this manner,” he says. “This is much more effective than the staining technique.”

What does the study claim?

According to the latest study published in the Lancet journal, which was conducted by researchers in the United Kingdom, the current methods of testing might need to be updated. The study notes that these methods might not be fast enough to pick up positive diagnoses which would be ideal in a country like India where a large population may be at risk of TB exposure. In India, a delay of a few days could have a significant impact on the overall presentation of tuberculosis in the country, according to several experts.

“The rapid blood tests which are mentioned in the study have not been endorsed by the WHO. These are just gross studies which have been done, we still need more evidence to support the same. The state and country will adopt more effective diagnostic tools if they are proven to be more accurate in picking up positive diagnoses,” adds Dr Anil.

On the other hand, others like Dr Roshan, feel that utilising a test like the geneXpert would result in more positive cases being detected and say that it is a more effective method in detecting resistant cases of TB as well. “GeneXpert can pick up cases which are resistant to rifampicin, the first choice drug for treatment of TB, this makes it a very effective tool to not only determine the presence of TB but also gives us a clue about what drug would be the best choice for treating the patient.”

What are the tools currently used for TB diagnosis in India and are they effective?

Sputum smear microscopy has long been the most commonly used technique to detect TB in the Indian healthcare set-up. It is also called ‘Acid-fast bacilli’ staining technique or AFB technique, AFB smear and culture, TB culture sensitivity test or AFB culture and sensitivity test.

“In the AFB technique, doctors collect sputum samples from patients on at least three different occasions. The collected specimen is then prepared for observation under the microscope in the form of a smear on a slide with certain dyes or stains. The infective organism in TB is Mycobacterium tuberculae which are acid-fast bacilli and will pick up the dye which can then be seen under the microscope,” explains Chennai-based physician Dr Keerthi Mohan.

At the same time, a culture is also prepared using the patient’s samples to see whether there is growth of the bacteria and to determine the most effective antibiotic.

Another test utilised is the Nucleic Acid Amplification Test (NAAT) or GeneXpert, sometimes also know as Polymerase Chain Reaction Assay (PCR Assay).

Though Dr Anil noted that the sputum smear microscopy, used most widely throughout the country, was effective, he acknowledged the benefits of the geneXpert test.

“The geneXpert can detect as few as 50 bacilli in the patient’s sample, whether it is a sputum sample, a tissue biopsy or CSF fluid. It is effective enough to pick up such low content of the TB-causing bacteria, allowing for a really early diagnosis of TB. This means that a patient may appear absolutely healthy, but their tests come out positive for TB. It’s an advantage to catch it so early, so that treatment can also be started early,” says Dr Anil.

However, the geneXpert test is still not used in all public healthcare facilities, though it has been deemed to be more effective. Sources from the National Tuberculosis Institute have stated that not all public healthcare centres may necessarily be equipped with the geneXpert equipment, adding that this itself could be a hindrance in eradicating TB.