AFB- detection of DNA by Real time PCR Tissue and biopsy
Biopsy0 parametersReport in 72HrsAt Home
No Fasting Required
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PCR test for Mycobacterium tuberculosis DNA in biopsy samples.
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AFB - Detection of DNA by Real Time PCR Tissue and Biopsy
- Why is it done?
- Detects Mycobacterium tuberculosis DNA in tissue and biopsy specimens using Real Time PCR (qPCR) technology for rapid and sensitive diagnosis of tuberculosis
- Diagnose active tuberculosis infection, particularly extrapulmonary TB (lymph nodes, organs, tissues, bones, central nervous system)
- Provide definitive diagnosis when histopathology shows caseating granulomas but AFB smear microscopy is negative or inconclusive
- Evaluate immunocompromised patients (HIV/AIDS) with suspected disseminated tuberculosis
- Differentiate tuberculosis from other granulomatous diseases (sarcoidosis, fungal infections, malignancy)
- Deliver faster results compared to traditional culture methods which can take 2-8 weeks
- Guide initiation of anti-tuberculous therapy in suspected cases, especially in critical conditions
- Normal Range
- Normal/Negative Result: No Mycobacterium tuberculosis DNA detected (Ct value >40 or undetectable) indicates absence of TB infection in the tissue sample
- Units of Measurement: Cycle Threshold (Ct) value or Quantification Cycle (Cq) value; qualitative reporting as Positive or Negative; quantitative results reported as copies/mL when applicable
- Interpretation Categories: Negative (Ct >40 or no amplification); Positive (Ct <40, typically <35); Borderline/Indeterminate (Ct 35-40 may require repeat testing)
- What Normal Means: Negative results suggest no active TB infection in the sampled tissue; however, does not exclude TB if clinical suspicion remains high
- What Abnormal Means: Positive result indicates presence of Mycobacterium tuberculosis DNA, confirming TB infection; requires clinical correlation with symptoms, imaging, and histopathology
- Interpretation
- Positive Result (Ct <40): Indicates active Mycobacterium tuberculosis infection; patient likely has TB and requires initiation of anti-tuberculous therapy; lower Ct values suggest higher bacterial load
- Negative Result (Ct >40): No TB DNA detected; TB infection unlikely in this tissue sample; consider alternative diagnoses if clinical presentation suggests TB; repeat testing may be warranted with fresh specimens
- Borderline/Indeterminate (Ct 35-40): Results near the cutoff threshold; should be interpreted cautiously; repeat testing, improved sample quality, or clinical reassessment recommended
- Factors Affecting Interpretation: Sample quality and quantity; timing of specimen collection; patient immune status; prior TB treatment; contamination during collection or processing; presence of PCR inhibitors
- Sensitivity and Specificity: Real Time PCR typically shows 85-95% sensitivity and 90-99% specificity for TB detection in tissue; variations depend on tissue type and bacterial load; better performance in lymph node and abscess specimens compared to other tissues
- Clinical Correlation Essential: Results must be interpreted with clinical symptoms, radiological findings, tuberculin skin test (TST) or interferon-gamma release assay (IGRA), histopathology, and AFB microscopy results
- Associated Organs
- Primary Organ Systems Involved: Respiratory system (lungs); lymphatic system (lymph nodes); central nervous system (meninges); musculoskeletal system (bones, vertebrae); gastrointestinal tract; genito-urinary system; other organs in disseminated TB
- Diseases Diagnosed or Monitored: Pulmonary tuberculosis; tuberculosis lymphadenitis; tuberculous meningitis; skeletal TB (Pott's disease); abdominal TB; cutaneous TB; urogenital TB; miliary (disseminated) TB
- Common Associated Conditions: HIV/AIDS with opportunistic TB infection; caseating granulomas on histology; constitutional symptoms (fever, night sweats, weight loss); chronic inflammation; lymphadenopathy
- Potential Complications of Abnormal Results: If TB confirmed: organ-specific damage (lung cavitation, neurological impairment in TB meningitis, spinal cord compression in Pott's disease); systemic dissemination; multi-drug resistant TB (MDR-TB); treatment-related side effects
- Differential Diagnoses to Consider: Sarcoidosis; fungal infections (histoplasmosis, coccidioidomycosis); atypical mycobacterial infections (MAC, NTM); malignancy; other granulomatous diseases
- Follow-up Tests
- If Result is Positive: Mycobacterial culture for species confirmation and drug susceptibility testing (DST); rifampicin and isoniazid resistance detection; fluoroquinolone resistance testing; Line Probe Assay (LPA) for rapid DST; drug-resistant TB panel if MDR-TB suspected
- If Result is Negative but Clinical Suspicion High: Repeat tissue biopsy or PCR testing; culture on Löwenstein-Jensen (LJ) or MGIT media; AFB smear microscopy; chest imaging (X-ray, CT); tuberculin skin test (TST) or interferon-gamma release assay (IGRA); serology if available
- Additional Diagnostic Tests: GeneXpert MTB/RIF for rapid TB and rifampicin resistance detection; NAAT (Nucleic Acid Amplification Tests); immunohistochemistry (IHC) staining; next-generation sequencing (NGS) for comprehensive mycobacterial characterization
- Complementary Tests: Immunological tests (CD4 count, HIV testing); liver and kidney function tests (baseline before anti-TB therapy); baseline audiometry (for aminoglycoside monitoring); retinopathy screening (for ethambutol)
- Monitoring During Treatment: Sputum AFB microscopy and culture (monthly); chest imaging (at completion of therapy); clinical assessment at 2, 4, and 8 weeks; repeat tissue biopsies if treatment failure suspected
- Post-Treatment Follow-up: Imaging studies to assess resolution; clinical examination at regular intervals; TST or IGRA (may remain positive indefinitely post-treatment); sputum AFB microscopy at end of therapy; screening for TB recurrence
- Fasting Required?
- Fasting Required: NO - Fasting is not required for this test as it involves tissue or biopsy specimen analysis, not blood sampling
- Sample Collection Requirements: Fresh tissue or biopsy specimen obtained through surgical or needle biopsy; minimum 50-100 mg tissue recommended; immediate fixation in appropriate preservative (10% neutral buffered formalin or sterile saline depending on laboratory protocol)
- Pre-Procedure Instructions: Consent for biopsy procedure; inform about procedure risks and benefits; patient may eat and drink normally unless biopsy is under general anesthesia (follow anesthesia fasting guidelines); continue regular medications unless instructed otherwise
- Medications: Continue regular medications; anticoagulants (warfarin, aspirin, DOAC) may need adjustment if invasive biopsy planned; notify physician of current antibiotic therapy as it may affect PCR results if specimens were taken during active treatment
- Special Specimen Handling: Sterile collection containers; avoid contamination with non-sterile material; rapid transport to laboratory (preferably within 2-4 hours); proper labeling with patient identification and collection time; temperature control if specified by laboratory
- Post-Procedure Care: Rest as advised; monitor biopsy site for infection or bleeding; follow wound care instructions; report any excessive pain, fever, or drainage; normal dietary intake immediately after procedure unless otherwise specified
How our test process works!
