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Testing & diagnosis of TB in India – CB-NAAT, Culture

The Standards for TB care in India (STCI) is the document that sets out how testing for TB and the diagnosing of TB should take place in India. The STCI was published in 2014 and it describes the TB testing and diagnosis that should be provided by the government’s Revised National TB Control Program (RNTCP) for all those suspected of having TB. This includes those in special categories, such as those with TB and HIV co-infection.

Subsequently the Technical & Operational Guidelines for Tuberculosis Control in India 2016 was launched. This document does not replace the STCI. However, it does update it as well as expand it. In particular it makes it clear that the STCI applies to all patients including those in the private sector.

Testing & screening for Pulmonary TB

Testing for pulmonary TB

Any person who has signs and symptoms suggestive of TB including a cough for more than 2 weeks, and a fever for more than 2 weeks, significant weight loss, haemoptysis (coughing blood) etc. and any abnormality in a chest radiograph should be evaluated to find out if the have TB.

Children with a persistent fever and/or cough for more than 2 weeks, children who have a loss of weight or no weight gain, and/or children who are household contacts of people who have already been diagnosed as having pulmonary TB must be evaluated for TB.

Screening for TB

People living with HIV (PLHIV), people who are malnourished, who have diabetes or cancer, and people on steroid therapy should be regularly screened for signs and symptoms suggestive of TB. Enhanced case finding should be undertaken in certain “high risk” populations such as healthcare workers, prisoners, slum dwellers. There should also be enhanced case finding in certain occupational groups such as mineworkers, as in some countries  such as South Africa, there is known to be a high level of TB among miners.

Enhanced case finding means having a high level of suspicion for TB in all encounters. Then excluding TB (or indeed identifying TB) using a combination of clinical queries, radiographic and microbiologic testing.

Diagnosis of TB in India

There are a number of diagnostic TB tests currently available. These include:

Microbiological confirmation on sputum:

All patients who have presumptive (that is are presumed to have) TB and who are capable of producing sputum, should undergo a sputum test for rapid microbiological diagnosis of TB.

Chest X-ray as a screening tool:

Where available chest X-ray should be used as a screening tool.

Cartridge Based Nucleic Acid Amplification Test (CB NAAT)

The CB NAAT is known as the GeneXpert in most countries other than India. This is the preferred first diagnostic test in children and people with TB and HIV co-infection.

Other TB tests

Serological tests for TB are banned and are not recommended for diagnosing TB. Neither are the Tuberculin Skin Test (TST) & Interferon Gamma Release Assays (IGRA)s. There are further descriptions of the tests for TB.

Sputum Samples

Sputum tests are very important in diagnosing TB, so paying attention to the detail of collecting a good sputum sample is very important. A number of studies have looked at this, and the general view is that two samples are almost as good as three samples.

Binocular microscopes are used for testing TB samples and the diagnosis of TB in India

Binocular microscopes are used for testing TB samples and the diagnosis of TB in India

Methods of testing using sputum samples include sputum smear microscopy (both conventional and fluorescent), culture (on solid or liquid media) commercial line probe asssay (LPA) or CB-NAAT.

With the advent of CB_NAAT the sensitivity and specificity of rapid diagnosis from sputum, has increased to approximately the levels seen in solid-media sputum culture. Of course the time scales, at just a few hours, are very much shorter with CB-NAAT.

There are also now starting to be some alternatives such as the TrueNat test. As this test has been developed in India it should be cheaper

RNTCP Laboratory Network

The RNTCP has established a network of laboratories where TB tests can be done to diagnose people who have TB. There are also tests that can be done to determine whether a person has drug resistant TB.

The laboratory system comprises National Reference Laboratories (NRLs), state level Intermediate Reference Laboratories (IRLs), Culture & Drug Susceptibility Testing (C & DST) laboratories and Designated Microscopy Centres (DMCs).

You can read more by looking at:

TB in India

or TB treatment in India

Major Sources for TB testing & diagnosis in India

RNTCP Technical and Operational Guidelines for TB Control in India 2016 www.tbcindia.nic.in

Standards for TB Care in India www.tbcindia.nic.in

RNTCP National Strategic Plan 2017 – 2025  www.tbcindia.nic.in