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AFB-DNA (TB-PCR) Detection by RTPCR, Reflex to Rifampicin resistance by Ultra CBNAAT (Sputum)

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Sputum PCR + CBNAAT detecting TB DNA and rifampicin resistance.

₹2,442₹3,489

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AFB-DNA (TB-PCR) Detection by RTPCR Reflex to Rifampicin resistance by Ultra CBNAAT (Sputum)

  • Why is it done?
    • Test Purpose: This test detects Mycobacterium tuberculosis DNA using reverse transcription PCR (RTPCR) technology and simultaneously assesses rifampicin resistance using Ultra CBNAAT (Cartridge Based Nucleic Acid Amplification Test) from sputum samples.
    • Primary Indications for Ordering: Suspected active pulmonary tuberculosis with need for rapid diagnosis and drug resistance profile
    • Clinical Scenarios: Patients with respiratory symptoms (persistent cough >2-3 weeks, hemoptysis, chest pain); individuals with TB risk factors (immunosuppressed patients, HIV+, close TB contacts); monitoring treatment response; screening suspected MDR-TB cases
    • Timing of Test: Performed as initial diagnostic test; can be repeated at 2 months to confirm cure; used at any point during TB treatment evaluation or when rifampicin resistance is suspected
  • Normal Range
    • Normal Result: NEGATIVE (No MTB DNA detected; No Rifampicin resistance detected)
    • Abnormal Results: MTB DETECTED (MTB DNA present - indicates active TB infection) or MTB DETECTED + RIF RESISTANT (TB with rifampicin resistance - indicates MDR-TB)
    • Result Categories: NEGATIVE | POSITIVE (MTB) | POSITIVE (MTB + RIF-R) | POSITIVE (MTB + RIF-S) | INCONCLUSIVE/ERROR
    • Units: Qualitative (Presence/Absence of MTB DNA; Presence/Absence of RIF resistance mutation)
    • Sensitivity & Specificity: RTPCR sensitivity 95-98% for smear-positive TB, 80-90% for smear-negative TB; specificity >99%; CBNAAT sensitivity 98% with >99% specificity for rifampicin resistance detection
  • Interpretation
    • NEGATIVE Result: No MTB DNA detected in sputum sample. Suggests absence of active pulmonary tuberculosis. Patient unlikely to have TB unless clinical suspicion remains high (may indicate early disease, insufficient sample, or extrapulmonary TB). Repeat testing may be recommended if clinical symptoms persist.
    • MTB DETECTED (Rifampicin Sensitive): Confirms active pulmonary TB with drug susceptibility. Patient has TB responsive to standard first-line therapy (HRZE regimen). Indicates non-drug-resistant TB. Patient can proceed with conventional TB treatment protocols.
    • MTB DETECTED + RIF-RESISTANT: Confirms active pulmonary TB with rifampicin resistance. Indicates multi-drug resistant tuberculosis (MDR-TB) or possible extensively drug-resistant TB (XDR-TB). Requires urgent initiation of second-line anti-TB drugs (fluoroquinolone + injectable agent + bedaquiline). Necessitates strict infection control measures and specialist TB management. Carries higher morbidity and mortality risk.
    • INCONCLUSIVE/ERROR Result: Test failed to produce valid result due to technical error, inhibitors, or sample quality issues. Requires recollection and repeat testing. Sample may have been inadequate, contaminated, or degraded.
    • Factors Affecting Results: Sample quality and adequacy, timing of collection during disease course, presence of inhibitors, concurrent infections, previous TB treatment status, specimen storage conditions, immunocompromised state (affects bacterial load), antibiotic use before sample collection
    • Clinical Significance of Patterns: Negative test in high-clinical-suspicion cases may indicate early TB, paucibacillary disease, or technical issues requiring clinical correlation and possible repeat testing. Positive MTB with RIF-sensitivity confirms standard TB treatment efficacy. Positive MTB with RIF-resistance indicates treatment failure with standard regimen and requires immediate intervention with second-line drugs to prevent treatment failure and transmission.
  • Associated Organs
    • Primary Organ System: Respiratory system (lungs, bronchi, trachea); also involves lymphatic system and lymph nodes
    • Diseases and Conditions Diagnosed: Pulmonary tuberculosis (active disease), multi-drug resistant TB (MDR-TB), rifampicin-resistant TB, extensively drug-resistant TB (XDR-TB), TB recurrence post-treatment
    • Potential Complications of Abnormal Results: Progressive lung tissue destruction and cavitation; respiratory failure; hemoptysis; spontaneous pneumothorax; bronchiectasis; chronic respiratory insufficiency; dissemination to other organs (TB meningitis, miliary TB); increased mortality risk with delayed MDR-TB diagnosis; treatment failure and development of XDR-TB; persistent transmission to contacts
    • Systems Potentially Affected: Pulmonary, cardiovascular (cor pulmonale), central nervous system (TB meningitis), renal, hepatic, gastrointestinal, musculoskeletal (Poncet disease), immune system
    • Associated Medical Conditions: HIV/AIDS, diabetes mellitus, malnutrition, alcoholism, smoking, silicosis, chronic lung disease, immunosuppression (malignancy, biologics), end-stage renal disease
  • Follow-up Tests
    • If MTB Positive (Drug-Sensitive): Chest X-ray to assess extent of lung involvement; CT thorax if needed for complications; Baseline liver and kidney function tests (LFT, RFT) before starting anti-TB drugs; baseline platelet count; baseline visual acuity and color vision (if ethambutol used); HIV testing (if status unknown); repeat AFB-DNA/sputum smear at 2 months (to confirm treatment response); monthly sputum smear examination for first 2-3 months
    • If MTB Positive + RIF-Resistant (MDR-TB): Urgent full drug susceptibility testing (DST) for all first-line and second-line drugs (Fluoroquinolones, Injectable agents, Bedaquiline, Linezolid); XDR-TB confirmation testing; Chest CT for detailed lung assessment; Comprehensive baseline investigations (LFT, RFT, electrolytes, baseline hearing assessment, baseline ECG for QTc interval); HIV testing; Audiometry if injectable agents planned; Repeat AFB-DNA/sputum smear at 1 month (baseline for monitoring); Contact tracing and preventive therapy assessment; Referral to TB specialist center
    • If Negative but High Clinical Suspicion: Repeat sputum samples on consecutive days (collect 2-3 samples); Consider early morning samples; Bronchoscopy with BAL if unable to obtain sputum; TB culture and susceptibility testing (gold standard but slower); Chest X-ray to assess for radiological TB
    • Monitoring During Treatment: Sputum AFB-DNA/smear microscopy at 1 month, 2 months, and end of intensive phase; LFT and RFT monthly during first 3 months; Repeat at 3 months and 6 months; Chest X-ray at end of intensive phase and end of treatment; Audiometry monthly (if on injectable agents); ECG if QT-prolonging drugs used; Clinical assessment for adverse drug reactions at each visit
    • Complementary/Related Tests: TB Culture (Lowenstein-Jensen medium or MGIT); Smear microscopy (AFB staining with Ziehl-Neelsen); Interferon-Gamma Release Assays (IGRA); TB antigen detection; Molecular line probe assay (LPA); Next-generation sequencing for comprehensive resistance profile; Serodiagnostic tests (limited reliability); Chest imaging (X-ray, CT)
    • Post-Treatment Follow-up: Repeat AFB-DNA or TB culture at end of treatment to confirm cure; Clinical evaluation at 1 year and 2 years post-treatment; Chest X-ray at treatment completion; Long-term follow-up for relapse surveillance (especially for MDR-TB); Annual screening for TB recurrence in high-risk individuals
  • Fasting Required?
    • Fasting Requirement: NO - Fasting is NOT required for this test
    • Sample Collection Type: Sputum specimen (not blood) - collected by patient expectoration into sterile container
    • Patient Preparation Requirements: Early morning sputum sample preferred (when sputum is most abundant); Patient should brush teeth and rinse mouth with water (not mouthwash) before collection; Rinse with water to remove food particles but do not use antiseptic solutions; Provide patient with proper collection container; Instruct patient to cough deeply from chest to produce sputum (not saliva); Collect minimum 5-10 mL of sputum; Sample should be transported to laboratory promptly within 2 hours or refrigerated if delay anticipated; Label specimen clearly with patient details and time of collection
    • Medications to Avoid: No specific medications contraindicated before test; if patient is on anti-TB drugs, continue regular medications as prescribed; Inform laboratory if patient has recently received antibiotics (may affect bacterial culture yield but not PCR detection)
    • Special Instructions: Collect sputum in designated biohazard container; Handle with appropriate biosafety precautions (TB is airborne transmissible); Ensure sample does not contain saliva only; If patient unable to produce sputum spontaneously, may require sputum induction with nebulized saline; Specimen should be transported by trained personnel with proper containment; Inform patient about TB transmission and infection control measures; Advise proper respiratory hygiene (covering mouth when coughing); Explain importance of providing best-quality sample for accurate results

How our test process works!

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