TB diagnostic test developed in India has high accuracy, says WHO

Truenat can be used as an initial tool for diagnosing TB at primary, community health centres

January 18, 2020 08:17 pm | Updated 08:18 pm IST

Competitive edge:  Truenat has been found to have sensitivity and specificity comparable with the currently used molecular diagnostic test.

Competitive edge: Truenat has been found to have sensitivity and specificity comparable with the currently used molecular diagnostic test.

In a Rapid Communication published on January 14, the World Health Organization (WHO) had mentioned that the India-made Truenat MTB, a molecular diagnostic test to diagnose pulmonary and extrapulmonary TB and rifampicin-resistant TB, has high diagnostic accuracy.

Truenat MTB has “high diagnostic accuracy as initial test to diagnose TB and to sequentially detect rifampicin resistance”, says the WHO Communication. Truenat MTB will be used as an initial test to diagnose TB thus replacing sputum smear microscopy.

Truenat is developed by the Goa-based Molbio Diagnostics. The company was provided with technical assistance and resources by the Foundation for Innovative New Diagnostics (FIND) to help commercialise Truenat. Indian Council of Medical Research (ICMR) had assessed and validated the diagnostic tool.

“Truenat will be cheaper per test than Xpert. The equipment and cartridges cost more in the case of Xpert,” says Balaram Bhargava, Director-General of ICMR. “Truenat is robust and most suited for Indian conditions.”

“With its better sensitivity, Truenat can be used as the initial tool for TB diagnosis,” says Prof. Bhargava.

Besides others, a multi-centric, prospective field evaluation study was carried out in four countries — India, Ethiopia, Peru, Papua-New Guinea — involving 744 participants, with final results on bacteriological culture.

Higher sensitivity

While sputum microscopy has only about 50% sensitivity, Truenat has been found to have higher sensitivity and specificity. According to WHO, the overall sensitivity of the Truenat MTB assay is 83% and specificity is 99%. In the case of Truenat MTBPlus, which uses two targets to diagnose TB bacteria, the sensitivity increases to 89% and the specificity is 98%.

In comparison, Xpert, which is also a molecular diagnostic test and has been widely used across the world, the sensitivity is 85% and specificity is 98%.

In cases where the sample is found to be positive for TB, tests can be done to know if the TB bacteria are already resistant to rifampicin, a drug used as part of first-line TB treatment. Truenat MTB-RIF test for knowing rifampicin resistance has 93% sensitivity and 95% specificity.

According to the WHO, the accuracy to diagnose TB using Truenat and Truenat MTB Plus is comparable with Xpert and Xpert Ultra. Likewise, the accuracy to detect rifampicin resistance using Truenat MTB-RIF is comparable with Xpert and Xpert Ultra.

Beats smear microscopy

Based on data available from around 230 TB diagnosing units located in primary health centres and community health centres in Andhra Pradesh, scientists at the Chennai-based National Institute of Epidemiology found Truenat had better ability to diagnose more TB positive cases. “Compared with smear microscopy, there was 30% more number of positive cases diagnosed after Truenat was implemented in the 230-odd units,” says Manoj V. Murhekar, Director of NIE.

Battery operated

“Instead of smear microscopy, Truenat can be used as an initial and point-of-care tool for diagnosing TB,” says Dr. Murhekar. “Since not much expertise is needed to carry out the test, it can be used in peripheral units such as public and community health centres.”

While Xpert needs reliable electricity supply and air-conditioning, Truenat is battery operated and portable and so can be used in remote places. Truenat takes about 25 minutes to extract the DNA and another 35 minutes for TB diagnosis. Testing for rifampicin resistance takes an hour and is done only if the sample tests positive for TB. In the case of Xpert, it takes two hours to complete the TB diagnosis and test for rifampicin resistance.

Compared with a one ml of sputum sample required in the case of Xpert, only 0.5 ml sputum sample is needed for Truenat. In the case of TB positive samples, the actual bacterial load in 1 ml of sputum sample is given, while Xpert provides only a qualitative result.

Low cost

The main cost advantage while using Truenat will be in the manner the tests are carried out. Only when samples test positive for TB will the test for rifampicin resistance be carried out in the case of Truenat. This is unlike Xpert where both TB diagnosis and rifampicin resistance test are done at one go. Hence the use of reagents may be reduced, and this will help make the testing cheaper when Truenat is used.

Also, a peripheral-level TB test using Truenat will reduce the delay in diagnosis and when combined with improved treatment initiation rates will fare better compared with district-level Xpert testing. After all, early diagnosis and treatment initiation will help reduce TB transmission and incidence.

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