Easy-to-use tongue-swab TB test shows accuracy in India

Mumbai: Less than three months after the World Health Organisation (WHO) recommended tongue swabs to detect tuberculosis (TB), a portable molecular test validated in India may help bring faster and easier TB diagnosis, according to an international study involving Indian researchers published recently in the New England Journal of Medicine (NEJM).

For over 100 years until rapid molecular TB diagnostic tests came up, smear microscopy was the most common TB test. However, both depend on a patient’s ability to cough sputum — a task children and elderly find difficult. A tongue swab, in contrast, would be easy, though accuracy has been an issue so far.

Now, a test platform, called MiniDock MTB, was evaluated across seven countries, including India, where Christian Medical College Vellore was a participating centre. The battery-operated device could accurately detect TB from both sputum and tongue-swab samples within 12 to 25 minutes, said the NEJM paper.

“Among 1,380 participants analysed in the study, the test detected TB with 85.7% sensitivity using sputum swabs and 79.6% sensitivity using tongue swabs,” said Dr D J Christopher, head of pulmonary medicine at CMC Vellore and one of the study authors.

He said the biggest advantage of tongue swabs would be affordability and ease of use in peripheral healthcare settings. “At present, healthcare systems often use microscopy first and reserve advanced tests like GeneXpert for selected patients. This strategy misses many positive cases.”

MiniDock platform belongs to the family of nucleic acid amplification tests (NAATs), regarded as the gold standard for rapid TB diagnosis, but is cheaper than other options. While the study showed that tongue swabs are slightly less sensitive than sputum testing, they still met WHO standards, researchers said.

The WHO also mentioned an Indian company, Molbio Diagnostics, with reference to tongue swab tests. According to the company’s spokesperson, “Our Truenat test is among the few indigenous platforms already deployed at primary health centres, enabling TB testing closer to the patient. It’s designed to accommodate multiple sample types, including tongue swabs.”

Chest specialist Dr Yatin Dholakia said, “When we are chasing national elimination of TB, we need to identify as many cases as possible at the earliest.” Tongue swabs could act as a tool to widely check for the disease. “X-ray is also an option, but it’s not logistically easy and there is the risk of radiation. Tongue swab tests would be a good alternative,” he added.