TrueNat tests for tuberculosis and COVID-19

TrueNat for TB testing

TrueNat was initially developed for the diagnosis of tuberculosis (TB) and to look for rifampicin-resistant TB in patients.

The machine uses real-time PCR to look for the presence of the DNA of the TB causing bacteria Mycobacterium tuberculosis, in a person’s body fluids.

It can also look for the presence of rifampicin-resistant TB. The test for this is called TrueNat MTB-RIF Dx. Rifampicin is an antibiotic that is used for the treatment of various bacterial infections including tuberculosis. Rifampicin-resistant TB bacteria would not react to the administration of rifampicin so other drugs are needed to treat patients with this type of TB. This is significant because treating patients with the wrong antibiotics can increase the bacteria's resistance to medicines—this has become a major concern for modern medicine today.

Molbio also has two other TrueNat tests for TB called Truenat^TM MTB and Truenat^TM MTB plus that help in the detection and quantification of TB bacteria in the pulmonary (from the lungs) and extrapulmonary secretions (EPTB specimens) of the body. EPTB specimens include the cerebrospinal fluid (from the brain or spine), pleural fluids (from the layer that covers the lungs), synovial fluid (from the joints) and aspirated (drawn) from the lymph nodes.

In December 2019, TrueNat TB test got approved by the World Health Organization (WHO) for the diagnosis of active TB and rifampicin-resistant TB.

TrueNat does not require cold temperature to work, unlike the other rapid TB test Xpert® MTB/RIF approved by the WHO. The latter is also being used for COVID-19 diagnosis.

TrueNat for COVID-19 testing

The Indian Council of Medical Research (ICMR) validated the use of TrueNat for the diagnosis of COVID-19 in April 2020 and by May 2020, ICMR had approved the use of TrueNat-Beta CoV for screening and confirmatory testing of COVID-19.

Read more: TB and COVID-19

The COVID-19 TrueNat, TrueNat SARS-COV-2 and TrueNat-Beta CoV tests look for the RNA of the coronavirus SARS-COV-2 which causes COVID-19. These tests use samples taken with oropharyngeal or nasopharyngeal swabs, to check for the coronavirus infection.

Since coronavirus is an RNA virus, it requires an RT-PCR which will first convert its RNA to DNA and then amplify the DNA. A real-time RT-PCR often needs about 5-6 hours. A TrueNat test is hence much more rapid.

Before starting the test, the samples are mixed with a reagent that inactivates the virus. This helps reduce the risk of infection to the lab personnel. According to the ICMR guidelines released in May 2020, TrueNat for COVID-19 is to be done in two steps:

• The first step looks for the presence of the E gene of the SARS-COV-2 virus. This gene codes for the envelope (E) protein of the virus. Any sample that comes out to be negative for this gene is said to be a true negative.
• Those that do get positive results from this test then are moved to the second step, which looks for the presence of the RdRp (RNA-dependent RNA polymerase) gene.

Envelope protein in coronaviruses is a small protein that is involved in the formation of the viral envelope (the outermost layer of some viruses). It also plays a role in viral pathogenesis and infectivity. Studies show that if you remove the envelope of coronaviruses, it would affect their ability to cause inflammation and their ability to establish an infection.

RNA polymerase is the enzyme that helps the coronavirus make copies of itself once it is inside healthy cells. Those that test positive for RdRp are said to be true positives.

Read more: ELISA antibody test for COVID-19

You do not need any special preparations for the TrueNat test unless your doctor advises you to do something specifically.

However, before you go for this test, your doctor may ask you if you are taking any medicines or supplements.

A TrueNat test for TB requires a sputum sample and a TrueNat for COVID-19 is done using nasopharyngeal and oropharyngeal swabs. Here is how the samples are obtained:

Sputum sample:

You will be provided with a special container to collect the sample. Sputum samples are either collected in special areas in the hospital or outside to reduce the risk of transmission (spread of infection) to healthy people. You will be asked to rinse your mouth with water before sample collection so the sample is not contaminated by any mouth bacteria or food particles. To collect a sputum sample for TB testing:

• Take a few deep breaths.
• Put a tissue on your mouth and cough deeply; you should be able to feel your cough in your stomach.
• As soon as the sputum comes into your mouth, spit it in the provided container. The lab technician will tell you how much sputum is needed.
• Once you get enough of the sample, cover the container lid tightly and give it to the lab personnel.
• The lab technician may check the sputum sample for clarity. If he/she thinks the sample is contaminated or not right, you may have to give another sample

Read more: AFB culture test for TB

Nasopharyngeal swab

Here is how a nasopharyngeal swab is collected:

• Your doctor may ask you to blow out your nose to remove any extra mucous and then to tilt your head back a bit.
• He/she will insert a swab stick (a thin plastic stick with a polyester or rayon tip) into your nose until it hits the back of your nose and let it sit there for a few seconds so it can absorb secretions from your nose. (This may cause some discomfort.)
• Next, the doctor will slowly pull the swab out of your nose, put it in a vial and send it to a lab for analysis.

Oropharyngeal swab

An oropharyngeal swab is taken from the back of the mouth: the oropharynx. The swab is gently rotated over the area for a few seconds and then put in a sterile vial to be sent to a lab for testing.

Normal results:

A  normal result in a TrueNat test would be given as negative, which means the pathogen was not found in the given sample.

Abnormal results:

Abnormal results in a TrueNat test would be given as positive, which means the given sample had the suspected pathogen. In the case of TB, the TrueNat test also tells if you have a rifampicin-resistant TB bacteria.

Your doctor will give you appropriate treatment depending on the results of the test.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.