MDR & XDR is on the rise and is now a major concern. Therefore, a comprehensive TB diagnostic solution is essential.
GeneXpert
GeneXpert MTB/RIF may be used rather than conventional microscopy and culture as the initial diagnostic test in all adults presumed to have TB
- Rapid test for detection of M. tuberculosis genome and Rifampicin resistance (detects rpoB gene mutation)
- Can be performed on all samples: pulmonary & extra pulmonary
- Can be done in smear positive as well as smear negative samples
- Rifampicin resistance is a surrogate marker for MDR-TB in 95% of strains
- Rapid TAT: Reports available same day
GeneXpert
GeneXpert test is capable of detecting Rifampicin resistance with 95 % sensitivity and 98 % specificity
TB Culture
- TB Culture using MGIT BACTEC (Liquid Based System) is the Gold Standard in diagnosis of tuberculosis
- All samples- pulmonary & extra pulmonary can be cultured by MGIT BACTEC
- Offers high rate of isolation (with 14% more M. tuberculosis recovered) as compared to solid culture
- TAT using MGIT BACTEC is 14-15 days at the earliest
Positive cultures are preserved for 12 weeks to allow drug sensitivity testing
Ref.: WHO Xpert MTB/RIF implementation manual 2014
TB Drug Sensitivity
- Detection of drug resistance can be done using MGIT BACTEC and can be accomplished in 2-3 weeks (after a +ve TB culture)
- Susceptibility to 13 drugs
MDR-TB
- Multi drug-resistant TB: Resistant to Isoniazid (INH) and Rifampicin.
- WHO estimates that 2.2% of new pulmonary tuberculosis (PTB) cases and 15% of previously treated PTB cases in India have MDR-TB (Global Tuberculosis Control 2015, WHO, Geneva, 2015www.who.int/tb/publications/global_report/-)
XDR-TB
- Extensively drug-resistant TB: Resistant to
(1) INH and Rifampicin
(2) Fluoroquinolones- Moxifloxacin, Ciprofloxacin, Levofloxacin
(3) One of the Injectable drugs – Amikacin, Kanamycin, Capreomycin - The Drug Resistance Surveillance (DRS) survey in India found XDR-TB in 4% of the identified MDR-TB isolates.
- It is estimated that a minimum of 2,000 new cases of XDR-TB emerge in India annually. Ref:http://www.tbonline.info/media/uploads/documents/jmmdraft2015.pdf
MTB Detection Test/ TB PCR
- Test can be performed on paucibacillary extra pulmonary TB (10-15% of all TB cases) samples
- Targets IS6110 gene which is present in multiple (4-15) copies in TB genome, hence sensitivity increases in comparison to other gene targets
Line Probe Assay (HAINS Test)
- Rapid Test for Molecular detection of Mycobacterium tuberculosis genome & resistance to 1st line drugs (Rifampicin & Isoniazid) and 2nd line drugs like Flouroquinolones, Aminoglycosides & Ethambutol
- Line Probe Assay- line 1 (MDR screen): Performed on pulmonary samples and +ve TB cultures
- RpoB gene associated with Rifampicin resistance
- KatG and InhA gene associated with Isoniazid resistance \
- Line Probe Assay- line 2 (XDR screen): Performed on smear +ve pulmonary samples and +ve TB cultures
- GYR gene associated with Fluroquinolone resistance
- RRS gene associated with Aminoglycoside resistance
- EMB gene associated with Ethambutol resistance
- Results are available next day
Cytology/ Biopsy
- Gross examination procedure by dedicated histopathologist
- Application of stringent diagnostic criteria/protocols for reporting (as per CAP guidelines)
- Application of special stains-ZN stain
Adenosine Deaminase (ADA)
- Marker of T-cell activation and cell-mediated immune response helps differentiate tubercular from non-tubercular aetiology
- Rapid test useful in accurate and early diagnosis in patients with extra pulmonary tuberculosis
- ADA test showed 100 % sensitivity and 94.6% specificity in tubercular pleural, peritoneal and pericardial effusion with a cut of value of 40 U/L with mean value of 100 U/L, 92U/L and 90 U/L respectively.
Ref: [Indian J Tuberc 2006; 53:92-95]
Extra Pulmonary (Ascitic Fluid, Pleural Fluid & CSF)
Extra Pulmonary (Lymph Node Aspirate OR Tissue)
Pulmonary (Sputum/ BAL)
