The document discusses CBNAAT (Xpert MTB/RIF), a qualitative PCR test that detects Mycobacterium tuberculosis complex DNA and rifampin resistance mutations. It can aid in TB diagnosis when used with clinical findings. The test is intended for use on untreated or short-term treated patients. Positive results must be confirmed by a reference lab, and it does not provide rifampin susceptibility confirmation. Xpert MTB/RIF has high sensitivity and specificity compared to smear microscopy and culture, especially for smear-negative TB. It can also detect rifampin resistance and has applications for extrapulmonary TB diagnosis from various samples.

1. CBNAAT
(Mtb Xpert)
Dr. Ankur Gupta

2. Xpert MTB/RIF
• CBNAAT is a qualitative, nested real-time
polymerase chain reaction (PCR) in vitro
diagnostic test.
• Assay also detects the rifampin-resistance
associated mutations of the rpoB gene. sequence
of the rpoB gene, is probed with five molecular
beacons (Probes A – E)
• Aid in the diagnosis of PTB when used in
conjunction with clinical and other laboratory
findings

3. • Intended for use with specimens from
patients for whom
– There is clinical suspicion of tuberculosis (TB) and
– who have received no antituberculosis therapy, or
less than three days of therapy

4. • Specimens that have both MTB-complex DNA
and rifampin-resistance associated mutations
of the rpoB gene detected by the Xpert
MTB/RIF Assay must have results confirmed
by a reference laboratory.
• Xpert MTB/RIF Assay does not provide
confirmation of rifampin susceptibility

5. • The testing of either one or two sputum
specimens by the Xpert MTB/RIF Assay may
serve as an alternative to serial acid-fast
stained sputum smears as an aid in the
decision of whether continued infection
control precautions are warranted

6. Steps in using the Xpert MTB/RIF assay

7. Limitations
• Assay is not indicated for
– Patients being treated with ATT
– Monitor bacteriologic cure
– monitor response to therapy
• Negative test does not exclude the possibility
of isolating MTB-complex from the sputum
sample
• Positive test does not necessarily indicate the
presence of viable organisms

8. Limitations
• Xpert MTB/RIF Assay does not differentiate
between the species of the MTB-complex
• Culture must also be performed to determine
if mycobacteria other than tuberculosis
complex (MOTT) is present in addition to
MTB-complex.
• M. scrofulaceum when tested at concentration
of 108 CFU/mL produced a false positive Xpert
MTB/RIF Assay result.

12. Xpert vs culture--collection method

13. Xpert vs culture--specimen type

14. Xpert vs DST

15. Xpert in smear negative

17. XPERT sensitivity specificity
as a replacement test for
smear microscopy
(21 studies,8880 pts)
Pooled - 88% (84-92)
(vs 65% for ms)
as an add-on test following
microscopy
(23 studies,7151 pts)
Pooled – 68% (61-74) 99% (98-99)
Using Xpert MTB/RIF to
detect sm + culture + TB
(24 studies, 2071 pts)
98 % (97-98)
Using Xpert MTB/RIF to
detect sm – culture+ TB
(24 std 724 pts)
43-100 % 86-100%

18. Xpert Sensitivity Specificity
Xpert to detect PTB in HIV-
(9 studies 2555 pts)
56-100%
86% meta
96-100%
Xpert to detect PTB in HIV+
10 std, 2378 pts
0-100%
79% meta
92-100%
Using Xpert MTB/RIF to
detect rifampicin resistance
27 std,2969 pts
95% (9097%) 9% (97-99%)

19. Xpert MTB/RIF to diagnose EPTB and
R Resist
• lymph node TB in samples from biopsy or fine-
needle aspiration – Sen=84.9%, Spe=92.5%
• pleural TB in pleural fluid – Sen=43.7%,
Spe=98%.
• “Pleural fluid is not regarded as a suitable
specimen for the microbiological diagnosis of
pleural TB. Pleural biopsy is the preferred
sample type for diagnosing pleural TB. ”

20. Xpert MTB/RIF to diagnose EPTB and
R Resist
• TB in samples of CSF – Sen= 79.5%, Spe=98.6%
• TB in gastric fluid – Sen= 83.8%, Spe=98.1%
• TB in tissue samples – Sen= 81.2%, Spe=98.1%

21. XPERT ULTRA
• Xpert MTB/RIF Ultra can better diagnose TB in
children and people living with HIV
• WHO on 24/3/2017 issued a recommendation
that Ultra can be used as an alternative to the
existing Xpert MTB/RIF test for the diagnosis
of TB and detection of rifampicin resistance in
all settings

22. Higher sensitivity especially in smear-negative TB
cases ability of the assay to detect low numbers of
bacilli (16 bacilli per ml sputum compared to 131
per ml for Xpert® MTB/RIF).
Results in <80 minutes
• Increased accuracy of Rifampicin results
• Improved detection of mixed infections

23. • Thank You