AFB-M.Tb Detection with Rifampicin resistance by CBNAAT Pleural Fluid

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Detects TB and rifampicin resistance in pleural fluid.

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AFB-M.Tb Detection with Rifampicin resistance by CBNAAT Pleural Fluid

Why is it done?
- Detects Mycobacterium tuberculosis (M.Tb) in pleural fluid samples using Cartridge Based Nucleic Acid Amplification Test (CBNAAT) technology
- Simultaneously determines rifampicin resistance, which indicates multidrug-resistant tuberculosis (MDR-TB)
- Diagnoses tuberculous pleural effusion or pleuritis when tuberculosis affecting the pleura is suspected
- Ordered when patients present with pleural effusion and clinical/radiological evidence suggesting TB or extrapulmonary TB involvement
- Guides appropriate anti-TB therapy selection, especially in settings with high MDR-TB prevalence
- Performs rapid diagnosis (results within 2 hours) compared to conventional culture methods which take weeks
Normal Range
- Negative Result: No M.Tb detected and no rifampicin resistance detected - indicating absence of tuberculosis in pleural fluid
- M.Tb Positive with Rifampicin Sensitive: M.Tb detected and susceptible to rifampicin - indicates drug-susceptible TB
- M.Tb Positive with Rifampicin Resistant: M.Tb detected and resistant to rifampicin - indicates multidrug-resistant TB (MDR-TB) requiring second-line therapy
- Indeterminate: Test result inconclusive due to technical issues - sample should be recollected and retested
- Units: Qualitative results reported as positive/negative or susceptible/resistant
Interpretation
- Negative Result: TB is unlikely in the pleural space; however, does not completely exclude TB as sensitivity is approximately 54-80% depending on sample quality and disease stage. False negatives may occur in early disease or inadequate samples.
- M.Tb Positive, Rifampicin Sensitive: Confirms tuberculous pleuritis with drug-susceptible strain. Patient should receive standard first-line anti-TB therapy (HRZE regimen). Excellent prognosis with appropriate treatment.
- M.Tb Positive, Rifampicin Resistant: Indicates MDR-TB requiring second-line anti-TB agents including fluoroquinolones, injectable drugs, and newer agents. Requires immediate referral to TB specialist, extended treatment duration (20+ months), and careful monitoring for adverse effects.
- Factors Affecting Results: Sample quality and volume, contamination during collection, timing of sample (earlier in disease may have lower yield), host immune status (immunocompromised patients may have higher bacterial load), adequacy of sample processing
- Clinical Significance: CBNAAT has high specificity (>99%) making false positives rare. WHO-endorsed test with superior sensitivity to AFB microscopy. Enables rapid treatment initiation, reducing morbidity and mortality. Rifampicin resistance detection critical for preventing treatment failure and continued transmission.
Associated Organs
- Primary Organ System: Pleura and lungs (respiratory system); also involves lymphatic system and surrounding tissues
- Conditions Associated with Abnormal Results:
  - Tuberculous pleuritis/pleural effusion (most common extrapulmonary TB)
  - Multidrug-resistant tuberculosis (MDR-TB) with pleural involvement
  - Extensively drug-resistant TB (XDR-TB) - may show rifampicin resistance
  - Active pulmonary TB with lymphatic spread to pleura
- Diseases Diagnosed/Monitored:
  - Tuberculous pleural effusion
  - Extrapulmonary tuberculosis with pleural involvement
  - Multidrug-resistant tuberculosis requiring alternative therapy
- Potential Complications of Abnormal Results:
  - Respiratory compromise and dyspnea from pleural effusion
  - Pleural fibrosis and lung restriction if untreated
  - Delayed diagnosis and treatment initiation in negative cases may lead to disease progression
  - MDR-TB with rifampicin resistance: treatment failure, mortality, transmission of resistant organisms
Follow-up Tests
- If Test is Positive:
  - Pleural fluid culture and drug susceptibility testing (DST) for confirmation and detection of additional resistance patterns
  - Chest X-ray or CT thorax to evaluate extent of pleural effusion and underlying pulmonary disease
  - AFB smear microscopy of pleural fluid for confirmation and infectivity assessment
  - Sputum AFB smear and CBNAAT if patient is coughing (to confirm pulmonary involvement)
  - HIV testing and CD4+ count if status unknown
  - Screening for contacts of MDR-TB patient if rifampicin resistance detected
- If Test is Negative but TB Suspected:
  - Pleural fluid culture (gold standard but takes 2-8 weeks)
  - Pleural fluid adenosine deaminase (ADA) level - high ADA suggests TB
  - Repeat CBNAAT on fresh pleural fluid sample if clinically warranted
  - Sputum CBNAAT and smear if patient has productive cough
  - Pleural biopsy for histology and culture if suspicion remains high
- Monitoring During Treatment:
  - Monthly clinical assessment and chest imaging to monitor pleural effusion resolution
  - Sputum smear microscopy at 2, 5, and 6 months if pulmonary TB present
  - Baseline and periodic liver function tests (LFTs) and renal function due to hepatotoxicity risks of anti-TB drugs
  - More frequent monitoring for MDR-TB cases on second-line therapy
- Complementary Tests:
  - Pleural fluid LDH, protein, glucose for characterization of effusion
  - Interferon-gamma release assays (IGRAs) for TB infection confirmation
Fasting Required?
- No - This test does not require fasting as it involves analysis of pleural fluid obtained through thoracentesis, not blood samples
- Patient Preparation Requirements:
  - Informed consent required for thoracentesis procedure
  - Baseline coagulation studies (PT/INR, aPTT) should be reviewed before procedure if not recently done
  - Chest imaging (X-ray or ultrasound) needed to localize effusion and mark needle insertion site
  - Patient should sit upright or lie on side with arms crossed over chest during procedure
  - Medications: Anticoagulants/antiplatelet agents (aspirin, warfarin, clopidogrel) should be held 3-5 days before procedure if possible
  - Sample must be collected in sterile container; at least 40-50 mL pleural fluid recommended for optimal yield
  - Samples should be processed promptly (within 2-4 hours) or refrigerated if delay is anticipated
  - Post-procedure: Rest and monitoring for 1-2 hours; chest imaging repeated if pneumothorax suspected

How our test process works!