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

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Detect DNA of Mycobacterium tuberculosis and check rifampicin resistance

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AFB-DNA (TB-PCR) Detection by RTPCR Reflex to Rifampicin Resistance by Ultra CBNAAT (Tissue)

Why is it done?
- Primary Purpose: Detects Mycobacterium tuberculosis (MTB) DNA in tissue samples using Real-Time PCR (RTPCR) technology, with automatic reflex testing for rifampicin resistance detection using Ultra Cartridge-Based Nucleic Acid Amplification Test (CBNAAT)
- Diagnostic Indications: Suspected tuberculosis in tissue specimens from various organs including lymph nodes, bone, lung tissue, joint fluid, pericardium, meninges, and other extrapulmonary sites
- Clinical Scenarios: Patients with persistent fever, lymphadenopathy, granulomatous lesions on histopathology, or clinical features suggestive of extrapulmonary tuberculosis
- Drug Resistance Assessment: Automatically detects rifampicin resistance mutations to identify multi-drug resistant tuberculosis (MDR-TB) in positive samples
- Timing: Performed when tissue biopsy or surgical specimens are obtained for diagnostic or therapeutic purposes in patients with suspected tuberculosis
Normal Range
- Normal Result: NEGATIVE - No MTB DNA detected in the tissue sample
- Abnormal Result: POSITIVE - MTB DNA detected (indicates tuberculosis infection)
- Interpretation of Positive Results: • MTB POSITIVE, Rifampicin SENSITIVE: Confirms TB; patient susceptible to first-line drugs • MTB POSITIVE, Rifampicin RESISTANT: Confirms MDR-TB; requires second-line drug regimens • MTB POSITIVE, Rifampicin INDETERMINATE: Results inconclusive; repeat testing recommended
- Units: Qualitative result (Positive/Negative) with semi-quantitative Cycle Threshold (Ct) values indicating bacterial load
- Reference Standard: Negative for MTB DNA indicates absence of tuberculosis; no rifampicin resistance testing is performed on negative samples
Interpretation
- Negative Result Interpretation: No MTB DNA detected; tuberculosis unlikely in the sampled tissue. However, false negatives can occur with low bacterial load, inadequate sampling, or specimen degradation. Clinical correlation and additional investigations recommended if suspicion remains high.
- Positive & Rifampicin-Sensitive Result: Confirms tuberculosis with susceptibility to rifampicin and other first-line anti-tuberculous drugs (isoniazid, pyrazinamide, ethambutol). Standard 6-month therapy recommended. Patient remains infectious until bacteriologically cleared.
- Positive & Rifampicin-Resistant Result: Indicates Multi-Drug Resistant TB (MDR-TB); resistant to rifampicin with presumed isoniazid resistance. Requires specialized second-line drug regimens (fluoroquinolones, injectable agents, newer drugs). Extended treatment period (20+ months) necessary. Immediate infection control measures essential.
- Low Bacterial Load (High Ct Values): Positive result with delayed amplification indicates lower number of MTB organisms. May suggest lower disease burden or specimen quality issues. Clinical management remains the same, but repeat testing may be considered.
- Indeterminate Results: Rare but may occur due to technical issues, inhibitors in specimen, or marginal amplification. Repeat testing with new specimen or culture confirmation recommended.
- Factors Affecting Interpretation: • Specimen quality and adequacy of tissue sampling • Prior anti-tuberculous therapy affecting bacterial load • Tissue preservation and processing conditions • Presence of PCR inhibitors in specimen • Clinical immune status (immunocompromised patients may have lower detection rates) • Anatomical site of tissue collection
Associated Organs
- Primary Organ Systems: Lymphatic system, Musculoskeletal system (bone/joints), Central nervous system, Cardiopulmonary system, Genitourinary system, Gastrointestinal system
- Commonly Associated Diseases: • Extrapulmonary Tuberculosis (EPTB) - most common presentation • Lymph Node TB (most frequent site - 50% of EPTB cases) • Tuberculous Lymphadenitis • Bone and Joint TB (Pott's disease of spine, tuberculosis of long bones) • Tuberculous Meningitis (CNS involvement) • Pericardial TB and Tuberculous Pericarditis • Abdominal TB (intestinal and peritoneal involvement) • Genitourinary TB • Multi-Drug Resistant TB (MDR-TB)
- Diagnostic Significance: Test helps confirm tuberculosis diagnosis in tissue specimens where culture may take weeks to months. Rapid identification enables prompt initiation of appropriate therapy.
- Potential Complications with Abnormal Results: • Progressive tissue destruction and organ damage if treatment delayed • Spread of infection to other organ systems • Development of drug-resistant strains if inappropriate therapy • Immunological complications (immune reconstitution inflammatory syndrome) • Chronic sequelae and functional impairment (especially neurological or skeletal TB) • Transmission risk to close contacts if infectious disease protocols not followed
- Organ-Specific Implications: CNS TB may cause hydrocephalus and neurological deficits; Skeletal TB can lead to kyphosis and spinal cord compression; Cardiac TB may cause tamponade; Renal TB can result in chronic kidney disease
Follow-up Tests
- Confirmatory Testing: Mycobacterial culture (Gold standard) from same tissue specimen for definitive diagnosis and drug susceptibility testing (DST); AFB smear microscopy for bacillary load assessment
- Drug Susceptibility Testing: Full DST panel if rifampicin resistance detected to determine susceptibility to second-line agents (fluoroquinolones, linezolid, bedaquiline, etc.) for MDR-TB and XDR-TB management
- HIV Testing: All TB-positive patients should be tested for HIV co-infection, which impacts treatment approach and monitoring
- Hepatic and Renal Function Tests: Baseline assessment before initiating anti-TB therapy; LFTs, kidney function (creatinine, eGFR) essential for monitoring drug-related toxicity during treatment
- Histopathological Examination: Microscopic analysis of tissue for granulomatous inflammation, caseating necrosis, and identification of AFB staining (Ziehl-Neelsen or auramine-rhodamine staining)
- Imaging Studies: Chest X-ray (if pulmonary involvement suspected), CT/MRI for site-specific disease assessment (CNS TB requires neuroimaging; spinal TB requires MRI), ultrasound for abdominal TB evaluation
- Treatment Monitoring Tests: Repeat molecular testing of clinical specimens at 2 months to assess treatment response; sputum/CSF/fluid sampling based on site of disease
- Contact Tracing Investigations: TST (Tuberculin Skin Test) or IGRA (Interferon-Gamma Release Assay) for close contacts; TB screening for household and workplace contacts
- Monitoring Frequency: Clinical assessment every 2 weeks initially, then monthly; LFTs at baseline, 2 weeks, 2 months, and 6 months; End-of-treatment tests (clinical assessment, radiological evaluation, culture/PCR of appropriate specimens at 5-6 months)
Fasting Required?
- Fasting Requirement: NO - Fasting is NOT required for this test as it involves tissue biopsy/surgical specimen analysis rather than blood collection
- Specimen Collection Requirements: • Tissue specimen obtained via biopsy, surgical excision, or aspiration • Place specimen in sterile, non-formalin container for molecular testing • If formalin fixation required for histopathology, separate unfixed tissue in sterile saline or DNA preservative • Keep specimen at 2-8°C if transport delayed beyond 2 hours • Minimize storage time; ideally process within 24 hours of collection
- Patient Preparation for Biopsy: • NPO (nil per os) for 6-8 hours if procedural sedation required for tissue collection • Standard pre-procedure preparation based on biopsy route (lymph node biopsy, bone biopsy, etc.) • Informed consent for biopsy procedure • Baseline coagulation profile if bleeding risk present
- Medications - No Restrictions: No need to withhold routine medications for PCR testing itself; however, anticoagulants may need adjustment based on biopsy procedure requirements
- Special Precautions: • Use sterile technique during specimen collection to avoid contamination • Wear appropriate PPE (gloves, mask) due to infectious nature of TB • Clearly label specimen with patient identifiers and collection date/time • Document specimen type, anatomical site, and clinical indication • Communicate results to infection control team for appropriate isolation measures

How our test process works!