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🔬 AFB-DNA Detection by RT-PCR

(Reflex to Rifampicin Resistance via Ultra CBNAAT)

Parameter	Details
Test Type	Molecular (DNA-based) Real-Time PCR
Sample Types	Sputum, BAL, pus, CSF, lymph node aspirates, pleural/ascitic/pericardial fluid, tissue biopsies
Fasting Required?	❌ Not required
Turnaround Time	24–48 hours for RT-PCR; same-day for Ultra CBNAAT
Primary Purpose	Detect DNA of Mycobacterium tuberculosis and check rifampicin resistance
Disease Focus	Pulmonary and Extrapulmonary Tuberculosis
Reflex Action	If TB DNA is detected, sample automatically proceeds to Rifampicin resistance testing using Ultra CBNAAT

🧪 What is AFB-DNA RT-PCR?

Uses Real-Time Polymerase Chain Reaction (RT-PCR) to amplify MTB-specific DNA sequences, making it highly sensitive and specific.
Particularly useful for extrapulmonary TB where bacilli are few.
Requires less bacterial load compared to microscopy.

🔁 What is Reflex to Rifampicin Resistance via Ultra CBNAAT?

Ultra CBNAAT (GeneXpert MTB/RIF Ultra) is an enhanced, automated molecular test that:
- Confirms presence of Mycobacterium tuberculosis
- Detects Rifampicin resistance (a marker of multidrug-resistant TB)
If MTB DNA is detected in RT-PCR, the lab automatically triggers the CBNAAT module without needing a fresh sample.

📈 Result Interpretation

🔹 RT-PCR MTB Detection

Result	Meaning
Detected	MTB DNA present → Active or latent TB likely
Not Detected	MTB DNA absent → TB less likely (but not ruled out)
Indeterminate	Low DNA load or inhibitors present

🔹 Ultra CBNAAT Rifampicin Resistance

Result	Meaning
RIF Resistance Detected	Suggests MDR-TB; urgent treatment adjustment needed
RIF Resistance Not Detected	MTB sensitive to rifampicin
Invalid/Error	Sample issue or processing failure

🔍 Clinical Use Cases

⚠️ Strengths vs Limitations

Strengths	Limitations
✅ High sensitivity (esp. in smear-negative)	❌ Expensive compared to smear or culture
✅ Detects even low bacterial loads	❌ Does not test for resistance to other drugs
✅ Fast – Same-day results (CBNAAT)	❌ Cannot distinguish live vs dead bacteria
✅ Rifampicin resistance = MDR-TB flag	❌ Requires special cartridge-based instruments

🔗 Recommended Additional Tests

Test	Purpose
AFB Culture (MGIT)	Confirms live bacilli, checks full drug sensitivity profile
Chest X-ray / HRCT Chest	Evaluates extent of pulmonary involvement
ESR, CRP	Inflammation markers
LFT, RFT	Baseline assessment before anti-TB drugs
HIV Test	TB-HIV co-infection common in immunocompromised patients

✅ Summary Table

Test	AFB-DNA RT-PCR with Reflex to Ultra CBNAAT
Purpose	Detect MTB DNA and Rifampicin resistance
Sample Types	Sputum, CSF, fluids, tissue, pus, aspirates
Sensitivity	High (90–98%), especially useful in smear-negative cases
Reflex Test	Automatically triggers Ultra CBNAAT on positive DNA
Time Taken	6–48 hours depending on facility
Treatment Impact	Helps start correct drug regimen early

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