cobas® MTB-RIF/INH

Rapid resistance testing for proper therapy

cobas MTB-RIF/INH product image
Rapid resistance testing for proper therapy

Tuberculosis is a bacterial infection caused by species of the Mycobacterium tuberculosis (TB, MTB) complex. A drug resistant strain is defined as resistance to at least one primary drug used to treat tuberculosis. A multidrug resistant TB (MDR-TB) is defined as resistance to at least isoniazid and rifampicin, the two most effective anti-TB drugs, and an extensively drug resistant TB (XDR-TB) is defined as a MDR-TB strain with additional resistance to any fluoroquinolone and at least one additional Group A drug. In 2022, it was estimated that approximately 4% of incident new TB cases in the world had MDR/RR-TB1. The frequency of MDR-TB varies according to region and is higher among previously treated patients.

cobas® MTB-RIF/INH for use on the cobas® 5800/6800/8800 Systems is an automated, qualitative real-time PCR test designed as a reflex test together with cobas® MTB to detect Rifampicin-resistance associated mutations of the rpoB gene and Isoniazid-resistance associated mutations in the katG and inhA genes, of M. tuberculosis. The test is intended for use on either acid-fast bacilli (AFB) smear-positive or smear-negative, raw sputum, and digested and decontaminated (N-acetyl-L-cysteine/ NaOH treated) sputum and bronchial alveolar lavage (BAL) samples, that tested positive for M. tuberculosis complex by cobas® MTB. Detection of wild-type MTB complex DNA serves as Internal Control to monitor the entire sample preparation and PCR amplification process. In addition, the test utilizes a low titer positive and a negative control.

* https://www.tballiance.org/why-new-tb-drugs/antimicrobial-resistance Accessed November 2023.

Molecular diagnostic algorithm

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Molecular diagnostic algorithm

Enabling a complete diagnosis is critical to ensure proper therapy is initiated. When patient presents with symptoms of tuberculosis, the cobas® MTB test is performed. If positive, patient should be evaluated for drug resistance using cobas® MTB-RIF/INH test. If negative, the cobas® MAI test can be used to detect a nontuberculosis infection.

Enabling a complete diagnosis is critical to ensure proper therapy is initiated. When patient presents with symptoms of tuberculosis, the cobas® MTB test is performed. If positive, patient should be evaluated for drug resistance using cobas® MTB-RIF/INH test. If negative, the cobas® MAI test can be used to detect a nontuberculosis infection.

       
cobas® MTB if positive cobas® MTB-RIF/INH
if negative cobas® MAI
Intended use

cobas® MTB-RIF/INH for use on the cobas® 5800/6800/8800 Systems is an automated, qualitative in vitro diagnostic test, that utilizes real-time polymerase chain reaction (PCR), for the direct detection of rifampicin-resistance associated mutations of the rpoB gene, and isoniazid-resistance associated mutations in the katG and inhA genes, of Mycobacterium tuberculosis, from human respiratory specimens. The test is intended for use on either acid-fast bacilli (AFB) smear-positive or smear-negative, raw sputum, and digested and decontaminated (N-acetyl-L-cysteine/ NaOH treated) sputum and bronchoalveolar lavage (BAL) samples, that tested positive for Mycobacterium tuberculosis complex (MTBC) by cobas® MTB. This test is intended for use in conjunction with culture and drug susceptibility testing, and as a reflex test together with cobas® MTB, as an aid in the diagnosis of infection with a multidrug resistant M. tuberculosis (MDR-TB).

Specifications and analytical performance

  • Sample Volume

    Sputum ≥ 0.4mL, Sediment ≥ 0.2mL

  • Specimen Types

    Raw Sputum, Sputum Sediment, Bronchoalveolar lavage (BAL)

  • Patient Collection

    Providing sufficient patient sample was collected, the cobas® MTB-RIF/INH test can be run in conjunction with cobas® MTB and cobas® MAI tests without the duplication of the pre-analytic processing

  • Sample Processing

    Manual liquefaction and inactivation followed by sonication and automated amplification and detection on the cobas® 5800/6800/8800 Systems

  • PCR Target Regions

    Eighteen Rifampicin-resistance associated mutations (rpoB gene) and seven Isoniazid resistance associated mutations (katG gene and inhA gene promotor region) are detected by multiple primers and mutation specific probes.

  • Controls

    Internal Control ensures sample validity. Test specific Positive Control and buffer Negative Control ensures run validity.

  • Inclusivity

    rpoB gene mutations associated with rifampicin resistance:

    L511P, Q513K, Q513L, Q513P, D516V, D516Y, S522L, S522Q, H526D, H526L, H526N, H526R, H526Y, S531L, S531W, L533P

     

    katG gene mutations and inhA gene promoter region mutations associated with isoniazid resistance:

    katG gene: S315I, S315N, S315T, S315T2

    inhA gene promoter region: T-8A, T-8C, C-15T

     

    The inclusivity for two more rpoB gene mutations associated with rifampicin resistance – S522W and D516G – was verified by testing plasmids

  • Analytical Specificity

    A panel of 145 bacteria, fungi and viruses, including those commonly found in respiratory tract did not interfere with the test by generating false positive results

  • Analytical Sensitivity (Limit of Detection)

    RIF-resistant M. tuberculosis
    94.0 CFU/mL (sputum/BAL sediment)
    182 CFU/mL (raw sputum)

    INH-resistant M. tuberculosis
    12.6 CFU/mL (sputum/BAL sediment)
    27.5 CFU/mL (raw sputum)

  • Endogenous Interference

    Not affected by the presence of elevated levels of gastric juice, hemoglobin, human whole blood, human DNA, mucin, pus and saliva

  • Exogenous Interference

    Not affected by the presence of 48 drugs and over-the-counter substances

Clinical performance

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Clinical performance

Sensitivity and specificity of cobas® MTB-RIF/INH using clinical samples - RIF target - INH target

Sensitivity and specificity of cobas® MTB-RIF/INH using clinical samples - RIF target - INH target

    RIF target
Roche cobas® MTB-RIF/INH
INH target
Roche cobas® MTB-RIF/INH
Sensitivity Raw Sputum

116/120

96.7%

(91.7 - 99.1%)

150/154

97.4%

(93.5 - 99.3%)

Sediment

23/23

100%

(85.2 - 100%)

35/37

94.6%

(81.8 - 99.3%)

Combined

139/143

97.2%

(93.0 - 99.2%)

185/191

96.9%

(93.3 - 98.8%)

Specificity Raw Sputum

331/338

97.9%

(95.8 - 99.2%)

297/299

99.3%

(97.6 - 99.9%)

Sediment

219/220

99.5%

(97.5 - 100%)

206/207

99.5%

(97.3 - 100%)

Combined

550/558

98.6%

(97.2 - 99.4%)

503/506

99.4%

(98.3 - 99.9%)

Heteroresistance

 

The ability to detect mutant MTB in a mixed infection with wild-type MTB was confirmed by testing different mutant to wild-type ratios. Low concentration levels of MDR MTB culture isolate (~3 x LoD) in a background of up to 60% wild-type MTB are detected by cobas® MTB-RIF/INH in sputum and sediment samples.

Package inserts

Access package inserts through your country’s Roche Diagnostics Website.

Registration status

CE-IVD, not approved in the US

References

  1. Global tuberculosis report 2023. Geneva: World Health Organization; 2023. Licence: CC BY-NC-SA 3.0 IGO.