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.
World Health Organisation (WHO) endorses TrueNat test
In December 2019 WHO held a meeting of its Guidelines Development Group. This was to consider the latest evidence on the use of the Molbio TrueNat MTB/RIF test as well as the Xpert MTB Ultra.1Guideline Development Group meeting, 2019, https://www.who.int/tb/areas-of-work/laboratory/en/ The outcomes of the meeting will be disseminated as updated WHO guidelines by April 2020.
In the meantime WHO has issued a Rapid Communication on the use of Molecular Assays as initial tests for the diagnosis of tuberculosis and rifampicin resistance.2Rapid Communication: Molecular assays as initial tests for the diagnosis of tuberculosis and rifampicin resistance, 2020, https://apps.who.int/iris/handle/10665/330395
The performance of Truenat MTB, MTB Plus and MTB-RIF Dx assays show comparable accuracy to the Xpert MTB/RIF and the Xpert Ultra for TB detection (Truenat MTB and Truenat MTB Plus) and for sequential rifampicin resistance detection (Truenat MTB-Rif Dx).
The Truenat MTB and MTB Plus assays also show comparable accuracy to the TB-LAMP assay as replacement tests for sputum smear microscopy. The data for Truenat MTB-Rif shows similar accuracy to WHO-approved commercial line probe assays.
Dr Balram Bhargava, the Director General of the Indian Council of Medical Research, said that this endorsement of the technology by WHO would enable low and middle income countries to procure TrueNat for tuberculosis diagnosis and Rifampicin resistance, so supporting the elimination of the disease in developing countries.3WHO endorses tech developed by Indian scientists to detect TB, multi-drug resistant TB, 2020, https://health.economictimes.indiatimes.com/news/diagnostics/who-endorses-tech-developed-by-indian-scientists-to-detect-tb-multi-drug-resistant-tb/73298950
WHO also said that the evidence reviewed supported the continued use of Xpert MTB/RIF and Xpert Ultra as initial diagnostic tests for pulmonary TB in patients of all ages.
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?
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.
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. 4Mudur, G. S. “One-hour test for TB”,
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.
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.5“Cheaper, indigenous TB test enters final validation phase”, The Hindu, July 01,2017,
Genexpert versus TruNat
The Genexpert machine and the TrueNat machine are designed to be used in different circumstances. The TrueNat machine is more of a point of care machine, which is not fully automated. It 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.
“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%.6“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 then entered the final leg of performance validation and operational feasibility testing by the Indian Council of Medical Research (ICMR). ICMR planned 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)
This page was last updated in January 2020.
Author Annabel Kanabus
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