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TB testing & diagnosis of TB in India – CB-NAAT

The “Standards for TB care in India” sets out how TB testing and the diagnosis of TB should take place in India. The standards were published in 2014 and describe 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, including those in special categories, such as those with TB and HIV co-infection. It does not however explain the detail of exactly how the testing and diagnosis should be provided, as this information is given in guidelines from the Government of India (GoI)1National Strategic Plan (2012-2017) for Tuberculosis – Directorate of Health Services, Central TB Division, Ministry of Health & Family Welfare (MoHFW) Government of India, New Delhi, www.tbcindia.nic.in.

This page describes the TB testing and diagnosis that should be provided as set out in the Standards for TB care in India document.

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 know 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, but of course the time scales, at just a few hours, are very much shorter with CB-NAAT.

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).

Major Sources for TB in India

Draft 2015 report on Indian Revised National TB Control Programme from Joint Monitoring Mission www.tbonline.info/media/uploads/documents/jmmdraft2015.pdf

Revised National Tuberculosis Control Programme Guidelines on Programmatic Management of Drug Resistant TB (PMDT) in India www.tbcindia.nic.in

Revised National Tuberculosis Control Programme National Strategic Plan 2012-2017

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

TB India 2015 Revised National TB Control Programme Annual Status Report, New Delhi, 2015 www.tbcindia.nic.in

References

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1. National Strategic Plan (2012-2017) for Tuberculosis – Directorate of Health Services, Central TB Division, Ministry of Health & Family Welfare (MoHFW) Government of India, New Delhi, www.tbcindia.nic.in