AFB-M.Tb Detection with Rifampicin resistance by CBNAAT Sputum

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Detects pulmonary TB with rifampicin resistance.

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AFB-M.Tb Detection with Rifampicin Resistance by CBNAAT Sputum - Comprehensive Guide

Why is it done?
- Rapid detection of Mycobacterium tuberculosis (M.Tb) in sputum samples using Cartridge Based Nucleic Acid Amplification Test (CBNAAT) technology
- Simultaneous detection of rifampicin resistance to identify Multi-Drug Resistant Tuberculosis (MDR-TB) for appropriate treatment planning
- Diagnosis of active pulmonary tuberculosis in patients presenting with persistent cough (>2-3 weeks), fever, night sweats, weight loss, and hemoptysis
- Initial screening in high-risk populations including HIV-positive patients, immunocompromised individuals, healthcare workers, and contacts of TB patients
- Monitoring treatment response and detecting treatment failure or relapse in TB patients
- Faster alternative to conventional sputum smear microscopy, culture, and drug susceptibility testing with results available within 2 hours
Normal Range
- Result Interpretation: This test provides qualitative results (not quantitative values), reported as one of the following categories:
- NEGATIVE (Normal Result): No M.Tb detected in the sputum sample. Indicates absence of active tuberculosis disease (though does not completely rule out TB in some cases)
- M.Tb DETECTED, Rifampicin SUSCEPTIBLE: M.Tb is present in the sputum and is susceptible to rifampicin. Indicates drug-susceptible TB (DS-TB) requiring standard first-line anti-TB therapy
- M.Tb DETECTED, Rifampicin RESISTANT: M.Tb is present and resistant to rifampicin. Indicates MDR-TB (Multi-Drug Resistant TB) or possible XDR-TB (Extensively Drug-Resistant TB) requiring specialized second-line therapy
- INVALID/INCONCLUSIVE: Test result could not be determined; sample quality issue or technical error. Repeat testing is required
- Test Sensitivity: 98-99% for M.Tb detection in patients with TB disease
- Test Specificity: 98-100% for M.Tb detection and rifampicin resistance detection
Interpretation
- NEGATIVE Result:
  - No tuberculosis bacilli detected in the sample
  - Does not rule out TB completely - paucibacillary disease, non-pulmonary TB, or inadequate sputum sample may result in false negatives
  - Repeat testing may be recommended if clinical suspicion remains high or if patient is immunocompromised
- M.Tb DETECTED with Rifampicin SUSCEPTIBLE:
  - Confirms active pulmonary tuberculosis with drug-susceptible organism
  - Indicates patient is infectious and requires immediate isolation and standard first-line anti-TB treatment (HRZE - Isoniazid, Rifampicin, Pyrazinamide, Ethambutol)
  - Patient contacts should be investigated and considered for preventive therapy
  - Culture and drug susceptibility testing (DST) should still be performed for confirmation and detection of additional resistant patterns
- M.Tb DETECTED with Rifampicin RESISTANT:
  - Indicates MDR-TB (resistant to at least isoniazid and rifampicin) or possible XDR-TB (additionally resistant to fluoroquinolones and second-line injectable drugs)
  - Confirms active TB with drug resistance - urgent second-line anti-TB therapy required (typically 5-7 drug regimens for MDR-TB)
  - Associated with higher mortality, morbidity, and prolonged treatment duration compared to drug-susceptible TB
  - Culture and comprehensive DST for second-line drugs must be performed to guide therapy
  - Referred to TB specialist and may require hospitalization for isolation and intensive treatment
- Factors Affecting Result Interpretation:
  - Sample quality - inadequate sputum volume or poor-quality samples may cause false negatives
  - Timing of collection - early morning sputum samples are preferred for better yield
  - Disease stage - newly diagnosed cases have higher sensitivity than patients on treatment
  - Immunocompromised status - HIV/AIDS patients with low CD4 counts may have lower sensitivity due to paucibacillary disease
  - Laboratory technique - proper CBNAAT machine calibration and maintenance are essential for accurate results
Associated Organs
- Primary Organ System: Respiratory System
  - Lungs - primary site of M.Tb infection in pulmonary TB; test directly assesses lung sputum
  - Airways - progressive inflammation and cavitation of upper lung lobes
  - Pleura - may develop pleural effusion in advanced disease
- Conditions Diagnosed or Monitored:
  - Pulmonary Tuberculosis (active disease) - primary indication for this test
  - Multi-Drug Resistant TB (MDR-TB) - rifampicin and isoniazid resistant disease
  - Extensively Drug-Resistant TB (XDR-TB) - MDR-TB additionally resistant to fluoroquinolones and injectable agents
  - TB treatment failure and relapse - detecting persistent M.Tb despite therapy
  - TB-HIV co-infection - particularly important in immunocompromised patients with low CD4 counts
- Potential Complications and Associated Conditions:
  - Hemoptysis - coughing up blood due to cavitary lung disease
  - Respiratory failure - progressive lung damage leading to reduced lung function
  - Spontaneous pneumothorax - lung collapse from cavitary disease
  - Disseminated TB - hematogenous spread to other organs (liver, kidney, bone, CNS)
  - TB meningitis - CNS involvement with high mortality if untreated
  - Pulmonary fibrosis and emphysema - chronic lung damage from previous TB
Follow-up Tests
- If CBNAAT Result is POSITIVE:
  - Sputum Smear Microscopy (AFB/Auramine-Rhodamine) - Confirms CBNAAT result and determines bacillary load; graded as scanty, 1+, 2+, or 3+
  - Sputum Culture and Drug Susceptibility Testing (DST) - Gold standard for confirmation and comprehensive drug resistance pattern identification (culture takes 2-8 weeks)
  - Liquid Culture (MGIT) - Faster culture method for M.Tb growth and drug susceptibility
  - Line Probe Assay (LPA) - Rapid (2 days) identification of MDR-TB and detection of second-line drug resistance
  - Chest X-Ray - Assess extent of lung involvement, cavitation, and complications
  - HIV Testing - Recommended for all TB patients to guide co-management
  - Liver Function Tests (LFTs), Renal Function Tests (RFTs), and Complete Blood Count (CBC) - Baseline assessment before starting anti-TB therapy and monitoring during treatment
  - Contact Tracing - Tuberculin Skin Test (TST) or Interferon-Gamma Release Assay (IGRA) for family members and close contacts
- If CBNAAT Result is NEGATIVE:
  - Repeat CBNAAT - If clinical suspicion is high, repeat sputum samples on consecutive days may be recommended (2-3 samples)
  - Sputum Smear Microscopy - Confirm negativity by conventional AFB microscopy
  - Chest X-Ray - Rule out radiological TB changes and identify alternative diagnoses
  - Tuberculin Skin Test (TST) or IGRA - Identify latent TB infection if clinical presentation is suggestive
  - Bronchoscopy and Bronchoalveolar Lavage (BAL) - If non-pulmonary TB or endobronchial disease is suspected
  - CT Thorax - If diagnosis remains unclear after initial investigations
- Monitoring During and After Treatment:
  - Repeat CBNAAT after 2 months of treatment - Patient should ideally become CBNAAT negative (indicates treatment response)
  - Repeat CBNAAT/Sputum microscopy at months 4, 5, and 6 - To assess treatment response and detect treatment failure
  - End-of-treatment CBNAAT/Culture - Final confirmation of cure and absence of persistent infection
  - Post-treatment monitoring CBNAAT - May be performed if symptoms recur suggesting relapse or re-infection
  - Monthly LFTs and RFTs during treatment - To monitor for anti-TB drug hepatotoxicity and nephrotoxicity
  - Repeat Chest X-Ray - At 2 months and 6 months of treatment to assess radiological improvement
Fasting Required?
- Fasting Status: NO
- Fasting is NOT required for CBNAAT testing as this is a respiratory sputum-based test, not a blood test
- Sample Collection Instructions:
  - Early morning sputum sample is PREFERRED - Collect sputum after sleeping overnight as it tends to have higher bacterial yield
  - Adequate sputum volume - Minimum 2-3 mL of sputum (not saliva) should be collected in a sterile, leak-proof container
  - Patient should rinse mouth with water - Before collection to remove food particles and oral flora
  - Patient should cough deeply - Deep cough from lungs to produce genuine sputum (not saliva)
  - If unable to spontaneously produce sputum - Inhalation of normal saline aerosol (sputum induction) may be used to stimulate sputum production
- Sample Handling and Storage:
  - Samples should be transported to the laboratory immediately or within 2-3 hours of collection
  - Use appropriate biosafety containers - Sputum samples are infectious and require Level 2 biosafety handling
  - Room temperature storage is acceptable - If processing is delayed, store at room temperature (excessive refrigeration or heating should be avoided)
  - Samples are typically valid for 7 days when stored at room temperature
- Medications or Preparations to Avoid:
  - No specific medications need to be avoided before sample collection
  - Continue regular anti-TB therapy if already on treatment - This does not affect CBNAAT result interpretation
  - Mouthwash and lozenges should be avoided 30 minutes before collection - These may contaminate sputum with oral flora
- Other Patient Preparation Requirements:
  - Infection control - Use appropriate personal protective equipment (PPE) including N95 mask when handling patient with suspected TB
  - Patient education - Explain the importance of providing genuine sputum from the lungs and not saliva
  - Proper identification and labeling - Ensure accurate patient identification and specimen labeling to avoid mix-ups
  - Document clinical history - Provide information about TB symptoms duration, previous TB history, and HIV status (if known)
  - Note prior TB treatment status - Important for interpreting results as resistance patterns may differ in previously treated patients

How our test process works!