DIAGNOSTIC TOOLS FOR TUBERCULOSIS

DIAGNOSTIC TOOLS 

Tools for microbiological confirmation of TB

 All efforts should be undertaken for microbiologically confirming the diagnosis in presumptive TB patients. Under RNTCP, the acceptable methods for microbiological diagnosis of TB are:

Sputum Smear Microscopy (for AFB): 

Zeihl-Neelson 
Staining
Fluorescence staining

Culture : Solid (Lowenstein Jensen) media Automated Liquid culture systems e.g. BACTEC MGIT960, BactiAlertorVersatreketc. Drug Sensitivity Testing: Modified PST for MGIT 960 system (for both first and second line drugs) Economic variant of Proportion sensitivity testing (1 %) using LJ medium (as a back up when indicated)

Rapid molecular diagnostic testing: Line Probe Assay for MTB complex and detection of RIF& INH resistance NucleicAcid Amplification Test (NAAT) Xpert MTB/Rif testing using the GeneXpert system

Smear microscopy being the most commonly used method for microbiological diagnosis of TB for the last several decades, has had enormous value in TB diagnosis but with limited sensitivity, more so in children and PLHIV. Under RNTCP, two methods of microscopy are currently being used- ZN stain based microscopy using conventional microscope and Light Emitting Diode based Fluorescent Microscopy (LED FM).
Culture though highly sensitive and specific method for TB diagnosis, requires 2-8 weeks to 
yield  
results and hence alone does not help in early diagnosis. However culture will be used for follow up of patients on Drug Resistant TB treatment to detect early recurrence as part of using the indicator of relapse free cure.

NucleicAcid Amplification Test (NAAT) provides accurate and rapid diagnosis of TB by detecting Mycobacterium tuberculosis (M. tuberculosis) and Rifampicin (Rif) resistance conferring mutations, in sputum specimen as well as specimen from extra-pulmonary sites. Presently, under RNTCP, its use is recommended for diagnosis of DR-TB in presumptive DR-TB patients and TB preferentially in key population such as children, PLHIV and Extra-pulmonary TB.

Other  diagnostic tools 

Radiography
Where available, CXR to be used as a screening tool to increase sensitivity of the diagnostic algorithm. Any abnormality in chest radiograph should further be evaluated for TB including microbiological confirmation. In the absence of microbiological confirmation, careful clinical assessment for TB diagnosis should be done. Diagnosis ofTB based on X-ray will be termed as clinically diagnosed TB.

Tuberculin Skin Test (TST)& Interferon Gamma Release Assay (IGRA) 
Standardized TST may be used as complementary test in children in combination with microbiological investigations, history of contact, radiology and symptoms. Interferon-Gamma Release Assays (IGRAs) are being used in place of skin test in low prevalence countries to detect