AFB-Xpert panel (M.Tb Detection & Rifamipicin resistance) by CBNAAT - 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 by CBNAAT (Extrapulmonary Samples)
Parameter | Details |
|---|---|
Test Name | AFB-Xpert Panel (CBNAAT – GeneXpert MTB/RIF or Ultra) |
Methodology | Cartridge-Based Nucleic Acid Amplification Test (CBNAAT) |
Technology | Real-time PCR targeting M. tuberculosis DNA + rifampicin resistance genes |
Sample Type | Extrapulmonary: CSF, pleural fluid, ascitic fluid, pus, lymph node aspirate, biopsy, tissue, urine, BAL, etc. |
Fasting Required? | ❌ No fasting required |
Turnaround Time | ⏱️ Within 2–6 hours (automated results) |
Purpose | Detect active TB and rifampicin resistance in non-respiratory samples |
Target Organs | CNS, lymphatic system, GI tract, GU tract, bones/joints, peritoneum, etc. |
🔍 Why is CBNAAT Preferred in Extrapulmonary TB?
- Smear microscopy often negative due to low bacilli load in extrapulmonary sites.
- CBNAAT is 2–3x more sensitive than smear.
- Gives rapid diagnosis and resistance info from a single sample.
- Useful in children, HIV-positive, and immunocompromised patients.
📈 Result Interpretation
🔹 MTB Detection
Result | Meaning |
|---|---|
MTB Detected | TB DNA present → active TB likely |
MTB Not Detected | No DNA detected → TB less likely, but not ruled out (esp. if paucibacillary) |
Trace/Low Detected | Low DNA detected → consider clinical and radiological correlation |
🔹 Rifampicin Resistance
Result | Interpretation |
|---|---|
Resistant Detected | Likely MDR-TB → start second-line drugs |
Sensitive Detected | Responds to standard first-line anti-TB regimen |
Indeterminate/Invalid | May need repeat or culture confirmation |
⚕️ Common Clinical Scenarios for Use
Sample Type | Suspicion |
|---|---|
CSF | TB meningitis |
Lymph Node Aspirate | TB lymphadenitis (neck, axilla, groin) |
Pleural/Ascitic Fluid | TB pleuritis, TB peritonitis |
Pus | TB abscesses (cold abscess, spinal TB) |
Urine | Genitourinary TB |
Bone/Biopsy tissue | Skeletal TB (Pott’s spine, joint TB) |
🔬 Test Strengths vs Limitations
✅ Strengths | ⚠️ Limitations |
|---|---|
Highly sensitive for paucibacillary TB | Sensitivity lower in serous fluids like pleural/ascitic |
Detects rifampicin resistance rapidly | May need culture if resistance confirmation required |
Results within 2–6 hours | Doesn’t detect resistance to other drugs (INH, FQ, etc.) |
Applicable to a wide variety of sample types | May require special sample handling or processing |
🔗 Recommended Further Diagnostics (if Positive or Inconclusive)
Test | Purpose |
|---|---|
MGIT Culture (Liquid culture) | Confirm live bacteria and test resistance to other drugs |
Line Probe Assay (LPA) | Identify mutations for isoniazid, fluoroquinolone resistance |
Histopathology (biopsy) | Granulomas in case of TB lymphadenitis or GI TB |
Imaging (CT/MRI) | Evaluate TB in brain, spine, abdomen, etc. |
ESR, CRP, CBC | Assess systemic inflammation |
HIV ELISA | TB-HIV co-infection is common and alters treatment pathway |
✅ Summary Table
Test | AFB-Xpert (CBNAAT – Extrapulmonary Samples) |
|---|---|
Purpose | Detect M. tuberculosis + Rifampicin resistance |
Sample Types | CSF, pus, ascitic/pleural fluid, LN aspirate, urine, tissue, BAL |
Sensitivity (vs Culture) | ~80–90% for pus/biopsy; lower for fluids |
Resistance Detection | Only rifampicin (first-line MDR marker) |
Turnaround Time | 2–6 hours |
WHO Recommendation | Preferred first-line test for extrapulmonary TB |
How our test process works!
