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TrueNat TB Test – Diagnosis and resistance testing

What is the TrueNat TB test?

The TrueNat TB test is a new molecular test that can diagnosis TB in one hour as well as testing for resistance to the drug rifampicin.

Sample loading for diagnosis of MTB using Trueprep-MAG device (TrueNat)

Sample loading for diagnosis of MTB using Trueprep-MAG device ( TrueNat )

Who has developed the TrueNat TB test?

The TrueNat test has been developed by the Indian firm MolBio Diagnostics Pvt Ltd Goa. It’s development has been funded by Bigtec Labs, India.

What sample is used for the test?

This test for TB uses a sputum sample taken from each patient. Only about 0.5 ml of the sample is required compared with about 1 ml needed for the American GeneXpert machine.

With this test samples can be tested as soon as a patient with symptoms of TB is seen. As the entire set-up is both battery operated and portable, it can be used at the most basic parts of the health care system. This is where this test differs from GeneXpert. GeneXpert is most suitable for being used where several tests can be done at the same time.1Chaitali, N et. al. “Evaluation of the Indian TrueNAT micro RT-PCR device with GeneXpert for case detection of pulmonary tuberculosis”, September 2014, www.researchgate.net/publication/8233_Evaluation_of_the_Indian_TrueNAT_micro_RT-PCR_device_with_GeneXpert_for_case_detection_of_pulmonary_tuberculosis

The standard smear microscopy test has limitations. It usually finds it difficult to diagnose TB when the bacterial load is less than 10,000 per millilitre of the sputum sample, giving erroneus negative results for some patients. 2Mudur, G. S. “One-hour test for TB”, https://www.telegraphindia.com/india/one-hour-test-for-tb-183556

How does the TrueNat test work?

The test works by the rapid detection of TB bacteria using the polymerase chain reaction (PCR) technique.

The machine looks for the DNA specific to the TB bacteria. If the machine detects it, it then uses PCR to copy (amplify) small segments of DNA and this DNA can then be used in many different laboratory procedures.

Addition of DNA to TrueNat MTB chip

Addition of DNA to TrueNat MTB chip

Any resistance to rifampicin (RR) is detected by doing a second RTPCR (Reverse transcription polymerase chain reaction)

Automated battery operated devices are used for the extraction of DNA (Trueprep Auto device) amplification (TrueNat MTB chip) and reading the presence of specific genomic sequences (TrueLab PCR analyser).

How long does it take to do a test?

It takes about 25 minutes to do the DNA extraction. It takes another 35 minutes to diagnose TB. It takes an additional one hour for testing for rifampicin resistance.3“Cheaper, indigenous TB test enters final validation phase”, The Hindu, July 01,2017, www.thehindu.com/sci-tech/health/cheaper-indigenous-tb-test-enters-final-validation-phase/article19193085.ece

Genexpert versus TruNat

The Genexpert machine and the TrueNat machine are designed to be sued in different circumstances. The TrueNat machine is more of a point of care machine, which is not fully automated and which is designed for situations where there may not be electricity and where the need is for one test to be done at a time.

The Genexpert is designed for larger volumes and needs a reliable electricity supply. Competition between manufacturers will hopefully bring down the price of doing tests with both machines in the next couple of years.

“We are not going to replace GeneXpert. We are planning to take Truenat MTB to the primary health centre level, which cannot be done using GeneXpert as it needs uninterrupted power supply and air conditioning.Dr Swaminathan, Director-General of ICMR

How far advanced is the testing of the TrueNat?

A preliminary test in 2013

In a preliminary test carried out on 191 patient samples in 2013, the sensitivity (ability of a test to correctly identify those with the disease) of TrueNat was found to be over 91% and the specificity (ability of the test to correctly identify those without the disease) was 100%.4“Rapid diagnosis of Mycobacterium tuberculosis with Truenat MTB: A Near-Care Approach”, Plos One, 2013, http://journals.plos.org/ It was concluded that:

“the TrueNat MTB test not only has good sensitivity and specificity for the diagnosis of TB but also fits the requirements of the resource limited settings. Large studies are required to obtain better estimates of the TrueNat MTB performance.”

 Performance validation & operational feasibility testing

The test is now entering the final leg of performance validation and operational feasibility testing by the Indian Council of Medical Research (ICMR). ICMR plans to take the test to Public Health Centres which currently use smear samples to test for TB.

“Besides validating the performance, the focus is on operational feasibility in field settings. We want to see if the machine performs to our satisfaction in hot and humid conditions and whether the machine can work even in the absence of power, and lab technicians with minimum training can operate the machine” Dr. N.S.Gomathi Chennai National Institute for Research in Tuberculosis (NIRT)

Marketing of the Truenat

In 2016 six TB-related Molbio Diagnostics products received CE-IVD marking. In addition these products have also been approved for use in India.

If the performance metrics from the ICMR study are successful then the products may be procured by the Indian public sector. The Molbio Diagnostics TB products are currently being evaluated by FIND. They intend to perform an accuracy study at three sites and they are also planning an operational assessment of the technology at the microscopy level.

Current prices offered by the company for the private market to procure the systems are US$7,000 and US$14 per assay and it is intended that public sectors will receive a further discount.5“Unitaid publishes its latest TB Diagnostic Technology Landscape report”, https://unitaid.eu/news-blog/unitaid-publishes-latest-tb-diagnostic-technology-landscape/#en

You can learn more about:

Testing for TB

Culture Test

Anti TB Drugs

References

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1. Chaitali, N et. al. “Evaluation of the Indian TrueNAT micro RT-PCR device with GeneXpert for case detection of pulmonary tuberculosis”, September 2014, www.researchgate.net/publication/8233_Evaluation_of_the_Indian_TrueNAT_micro_RT-PCR_device_with_GeneXpert_for_case_detection_of_pulmonary_tuberculosis
2. Mudur, G. S. “One-hour test for TB”, https://www.telegraphindia.com/india/one-hour-test-for-tb-183556
3. “Cheaper, indigenous TB test enters final validation phase”, The Hindu, July 01,2017, www.thehindu.com/sci-tech/health/cheaper-indigenous-tb-test-enters-final-validation-phase/article19193085.ece
4. “Rapid diagnosis of Mycobacterium tuberculosis with Truenat MTB: A Near-Care Approach”, Plos One, 2013, http://journals.plos.org/
5. “Unitaid publishes its latest TB Diagnostic Technology Landscape report”, https://unitaid.eu/news-blog/unitaid-publishes-latest-tb-diagnostic-technology-landscape/#en