AFB-Xpert panel (M.Tb Detection & Rifamipicin resistance) by CBNAAT - Extra pulmonary samples

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WHO-endorsed rapid diagnostic test for tuberculosis (TB), especially extrapulmonary TB where traditional methods often fail.

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AFB-Xpert panel (M.Tb Detection & Rifamipicin resistance) by CBNAAT - Extra pulmonary samples

Why is it done?
- Rapid detection of Mycobacterium tuberculosis (M.Tb) in extra pulmonary specimens using molecular testing (CBNAAT - Cartridge Based Nucleic Acid Amplification Test)
- Simultaneous detection of rifampin resistance, which indicates possible Multi-Drug Resistant Tuberculosis (MDR-TB)
- Diagnosis of extrapulmonary TB from samples such as cerebrospinal fluid (CSF), lymph node aspirates, joint fluid, pericardial fluid, abdominal fluid, blood, and other body fluids
- Provides results within 2 hours, enabling rapid diagnosis and initiation of appropriate TB treatment
- Indicated in patients with suspected extrapulmonary TB including TB meningitis, TB lymphadenitis, TB arthritis, and disseminated TB
- Useful in immunocompromised patients, including those with HIV/AIDS where extrapulmonary TB is common
Normal Range
- M.Tb Detection: NEGATIVE/NOT DETECTED - Indicates absence of Mycobacterium tuberculosis DNA in the sample
- Rifampin Resistance: NOT DETECTED/SUSCEPTIBLE - Indicates susceptibility to rifampin; bacteria are sensitive to the drug
- Result Categories:
- • NEGATIVE (Normal): No M.Tb detected; excludes active TB disease
- • POSITIVE (Abnormal): M.Tb detected; confirms TB disease
- • RIFAMPIN RESISTANT (Abnormal): M.Tb detected with RIF resistance; indicates MDR-TB; requires second-line drugs
- • INVALID/INDETERMINATE: Test failed; repeat testing recommended
- No quantitative values are reported; results are qualitative (presence or absence of M.Tb and RIF resistance)
Interpretation
- M.Tb NOT DETECTED & RIF Susceptible:
  - No evidence of active TB in the collected specimen
  - Alternative diagnoses should be considered
  - False negatives possible if specimen quality is poor or bacillary load is very low
- M.Tb DETECTED & RIF Susceptible:
  - Confirms diagnosis of extrapulmonary TB
  - Indicates drug-susceptible TB (DS-TB); standard first-line anti-TB therapy is appropriate
  - Immediate initiation of anti-TB treatment (RIPE regimen) recommended
- M.Tb DETECTED & RIF RESISTANT:
  - Confirms extrapulmonary TB with probable MDR-TB (Multi-Drug Resistant TB)
  - Requires immediate isolation and switch to second-line anti-TB drugs (fluoroquinolones, injectable agents, bedaquiline, linezolid)
  - Requires drug susceptibility testing (DST) for isoniazid and other agents to confirm MDR-TB and guide treatment
- Factors Affecting Results:
  - Specimen quality and quantity - poor samples may yield false negatives
  - Bacillary load - extrapulmonary samples often have lower bacterial counts than sputum
  - Proper sample collection and processing - critical for accuracy
  - Contamination - may affect result interpretation
  - Prior anti-TB treatment - may reduce bacterial detection
- Clinical Significance:
  - Sensitivity for extrapulmonary TB ranges from 55-80% depending on specimen type (CSF has higher sensitivity than other fluids)
  - Specificity is >99%, making positive results highly reliable for TB diagnosis
  - Rapid turnaround time enables prompt diagnosis and treatment initiation
  - Rifampin resistance detection is highly accurate for predicting MDR-TB status
Associated Organs
- Primary Systems Involved:
  - Central Nervous System (CNS) - particularly in TB meningitis
  - Lymphatic system - TB lymphadenitis
  - Skeletal system - TB arthritis, osteomyelitis
  - Cardiovascular system - TB pericarditis
  - Gastrointestinal system - TB peritonitis, abdominal TB
  - Genitourinary system - TB of kidney, bladder
- Common Diseases Associated with Abnormal Results:
  - Tuberculous meningitis (TB meningitis) - life-threatening CNS infection with high mortality
  - Tuberculous lymphadenitis - chronic lymph node inflammation
  - Poncet's disease (TB arthritis) - joint tuberculosis
  - Tuberculous pericarditis - cardiac TB with potential for tamponade
  - Tuberculous peritonitis - abdominal TB
  - Disseminated TB - widespread multiorgan disease
  - MDR-TB and XDR-TB infections - drug-resistant TB requiring specialized treatment
- Potential Complications of Abnormal Results:
  - TB meningitis - hydrocephalus, neurological deficits, permanent disability, death
  - Pericarditis - cardiac tamponade, constrictive pericarditis
  - Peritonitis - abdominal complications, malnutrition, bowel obstruction
  - Joint TB - permanent joint damage, functional impairment
  - MDR-TB complications - prolonged treatment, higher mortality, treatment failure
  - Disseminated disease - multi-organ involvement, severe immunocompromised state risk
Follow-up Tests
- Tests Recommended for Positive M.Tb Results:
  - Culture of M.Tb - gold standard for diagnosis, allows drug susceptibility testing (DST)
  - Drug Susceptibility Testing (DST) - determines sensitivity to first-line drugs (isoniazid, rifampin, ethambutol, pyrazinamide) and second-line drugs
  - Line Probe Assay (LPA) - rapid detection of MDR-TB and XDR-TB
  - Whole Genome Sequencing (WGS) - comprehensive drug resistance profiling
- Confirmatory and Diagnostic Tests:
  - AFB (Acid-Fast Bacilli) Microscopy - conventional staining and microscopic examination
  - TB-LAMP (Loop-mediated isothermal amplification) - alternative molecular test if CBNAAT unavailable
  - Histopathology - biopsy showing granulomatous inflammation, supportive of TB diagnosis
- Tests for Differential Diagnosis (if CBNAAT Negative):
  - CSF Analysis (protein, glucose, cell count) - for TB meningitis suspicion
  - Fluid Analysis (peritoneal, pericardial, synovial) - evaluate for other inflammatory causes
  - Interferon-Gamma Release Assay (IGRA) - tuberculin skin test (TST) or QuantiFERON Gold - assesses TB infection status
  - Imaging (CT/MRI) - assess extent of disease involvement
- Baseline/Concurrent Testing:
  - HIV Testing - extrapulmonary TB is common in HIV-positive patients
  - CD4 count (if HIV positive) - assess immunological status
  - Liver Function Tests (LFTs) - baseline assessment before anti-TB drug therapy
  - Renal Function Tests - baseline assessment before anti-TB drug therapy
- Monitoring During Treatment:
  - Repeat CBNAAT from new samples - to monitor treatment response (not for treatment adherence)
  - Periodic clinical assessment - evaluate symptom resolution
  - Imaging studies (CT/MRI) - assess radiological improvement at predetermined intervals
  - Monthly LFTs and renal function - monitor for anti-TB drug toxicity
Fasting Required?
- NO - Fasting is not required for this test
- Reason: This test analyzes extrapulmonary clinical specimens (body fluids, tissue aspirates) collected directly from the affected site, not blood. Food or fluid intake does not affect specimen collection or test results.
- Sample Collection Instructions:
  - Specimens collected using sterile technique by a qualified healthcare provider
  - Types of specimens accepted:
    - Cerebrospinal Fluid (CSF)
    - Lymph node aspirates (FNA)
    - Joint/synovial fluid
    - Pericardial fluid
    - Peritoneal fluid (ascitic fluid)
    - Pleural fluid
    - Tissue specimens/biopsy samples
    - Blood (when indicated)
  - Place specimen in sterile, leakproof container
  - Do NOT add fixatives or preservatives unless specifically instructed
  - Minimum volume: 1-2 mL (varies by specimen type)
  - Process and transport to laboratory within 2 hours at room temperature or refrigerate if delay anticipated
- Medications:
  - No medications need to be stopped or avoided specifically for this test
  - If patient is already on anti-TB treatment, inform the laboratory as this may affect result interpretation
  - Antibiotics taken prior to sampling may reduce bacterial recovery
- Other Patient Preparation:
  - No special preparation required for the patient
  - Specimen collection procedure will vary based on specimen type and site
  - For invasive procedures (lumbar puncture, aspiration, biopsy), informed consent required
  - Fasting may be required only if the collection procedure involves general anesthesia (as per anesthesia protocols)

How our test process works!