AFB Rapid culture by MGIT - Body Fluid

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No Fasting Required

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MGIT culture for TB detection in pleural, peritoneal, or CSF fluid.

₹1,169₹1,670

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AFB Rapid Culture by MGIT - Body Fluid

Why is it done?
- Detects and isolates Mycobacterium tuberculosis (MTB) and other acid-fast bacilli (AFB) from body fluids such as cerebrospinal fluid (CSF), pleural fluid, pericardial fluid, peritoneal fluid, and synovial fluid using the MGIT (Mycobacterial Growth Indicator Tube) system
- Diagnoses extrapulmonary tuberculosis (TB) including tuberculous meningitis, TB pleuritis, pericarditis, peritonitis, and arthritis
- Provides rapid culture-based confirmation of TB suspicion in immunocompromised patients, including those with HIV/AIDS
- Enables identification of MTB within 2-4 weeks (significantly faster than conventional methods)
- Allows drug susceptibility testing (DST) and identification of resistant strains
- Ordered when patients present with clinical signs of extrapulmonary TB such as persistent neurological symptoms, fever with pleural effusion, or joint inflammation
Normal Range
- Normal (Negative) Result: No growth detected in the MGIT medium; indicates absence of viable acid-fast bacilli in the body fluid sample
- Abnormal (Positive) Result: Growth of mycobacteria detected; indicates presence of viable AFB in the body fluid, confirming active mycobacterial infection
- Time to Positivity (TTP): Reported in days; typically 2-4 weeks for MTB; earlier positivity may indicate higher bacterial load
- Units: Qualitative result (Positive/Negative) or quantitative (growth units/CFU estimations when available)
- Interpretation: Negative results rule out TB in the cultured body fluid site; positive results confirm active mycobacterial infection requiring immediate treatment initiation
Interpretation
- Positive Culture Result:
  - Confirms diagnosis of extrapulmonary TB at the site of fluid collection
  - Speciation (identification of organism) and drug susceptibility testing (DST) will follow to determine antimicrobial resistance patterns
  - Requires immediate initiation or adjustment of anti-TB therapy
  - May indicate disseminated TB, particularly in immunocompromised patients
- Negative Culture Result:
  - Rules out viable mycobacterial infection in the cultured body fluid; does not exclude TB diagnosis if strong clinical suspicion exists
  - May reflect low bacterial burden, non-viable organisms, or improper specimen handling
  - Clinical correlation with imaging, histopathology, and other diagnostic tests remains essential
- Early Time to Positivity (TTP < 2 weeks):
  - Suggests high mycobacterial load indicating severe/active infection
  - Associated with worse prognosis in TB meningitis and disseminated TB
- Factors Affecting Results:
  - Quality and volume of specimen (minimum 1-2 mL recommended; larger volumes increase sensitivity)
  - Proper storage and timely transport to laboratory (ideally within 2 hours)
  - Prior anti-TB therapy may reduce culture sensitivity by inhibiting growth of viable organisms
  - Contamination with other organisms may inhibit mycobacterial growth
  - Immunosuppression status (HIV infection may correlate with bacterial load variations)
- Clinical Significance:
  - Gold standard for definitive diagnosis of extrapulmonary TB; superior diagnostic accuracy compared to direct microscopy alone
  - MGIT sensitivity ranges from 80-90% depending on specimen type and patient factors
  - Specificity approaches 99% when positive; significantly faster than solid media (Löwenstein-Jensen or Ogawa)
Associated Organs
- Central Nervous System (CNS):
  - CSF culture gold standard for diagnosing tuberculous meningitis (TB meningitis)
  - Most serious form of extrapulmonary TB; high mortality and morbidity if untreated
  - Can result in neurological complications including hydrocephalus, cranial nerve palsies, spinal cord involvement
- Respiratory System (Pleura):
  - Pleural fluid culture confirms TB pleuritis/pleural effusion
  - Complications include empyema, pleural thickening, restrictive lung disease
- Cardiovascular System (Pericardium):
  - Pericardial fluid culture diagnoses TB pericarditis
  - Risk of cardiac tamponade, constrictive pericarditis, myocardial involvement, sudden death
- Gastrointestinal System (Peritoneum):
  - Peritoneal fluid culture confirms TB peritonitis/abdominal TB
  - May lead to intestinal perforation, adhesions, malabsorption, peritoneal fibrosis
- Musculoskeletal System (Joints):
  - Synovial fluid culture diagnoses TB arthritis/Poncet's disease
  - Complications include joint destruction, ankylosis, functional disability
- Disseminated TB:
  - Multiple body fluids may be positive indicating miliary TB or hematogenous spread
  - Higher risk in immunocompromised patients (HIV/AIDS, immunosuppressive therapy)
  - Associated with high mortality if untreated or delayed treatment
Follow-up Tests
- When Culture is Positive:
  - Mycobacterial speciation and differentiation (to identify MTB vs. non-tuberculous mycobacteria)
  - Drug susceptibility testing (DST) including first-line drugs (isoniazid, rifampicin) and second-line drugs for MDR/XDR-TB assessment
  - Genotypic resistance detection and molecular line probe assays (for rapid detection of resistance mutations)
  - AFB microscopy of positive culture isolate (acid-fast staining for confirmation)
  - Contact tracing and epidemiological investigation to identify potential transmission sources
- When Culture is Negative but Clinical Suspicion Remains High:
  - Repeat collection of body fluid specimen (particularly for CSF - repeat lumbar puncture if clinically indicated)
  - AFB microscopy/smear examination with Ziehl-Neelsen or auramine-rhodamine staining
  - Nucleic acid amplification tests (NAATs) such as GeneXpert MTB/RIF for rapid MTB detection and rifampicin resistance
  - Histopathological examination with granuloma identification and AFB staining of biopsied tissue
  - Imaging studies (CT or MRI) based on affected body system
  - TB serology (though less reliable than culture/microscopy)
- Additional Related Tests:
  - Sputum AFB culture/smear (to assess pulmonary involvement concurrent with extrapulmonary disease)
  - Tuberculin skin test (TST/Mantoux test) or interferon-gamma release assays (IGRAs)
  - HIV testing (essential in extrapulmonary TB to determine immunosuppression level)
  - CD4 count and viral load in HIV-positive patients
  - Inflammatory markers (ESR, CRP) - monitor treatment response and disease activity
- Monitoring During Treatment:
  - Clinical assessment and symptom monitoring throughout 6-month (standard) or 9-month (MDR-TB) treatment course
  - Repeat body fluid cultures at 2-4 weeks if clinically indicated (may be delayed up to 6-8 weeks in meningitis)
  - Imaging follow-up at 2-3 months to assess response to therapy
  - Hepatic function tests (AST, ALT, bilirubin) if on hepatotoxic anti-TB medications
  - Renal function tests and uric acid levels during treatment
Fasting Required?
- Fasting Requirement: NO - fasting is NOT required for AFB culture by MGIT from body fluids
- Specimen Collection Procedure:
  - CSF: Collected via lumbar puncture (LP) - sterile, atraumatic procedure; minimum 1-2 mL recommended (preferably 5-10 mL for optimal yield)
  - Pleural Fluid: Collected via thoracentesis - minimum 40-50 mL in sterile container for optimal culture recovery
  - Pericardial Fluid: Collected via pericardiocentesis under ultrasound guidance; 10-50 mL recommended
  - Peritoneal Fluid: Collected via paracentesis; minimum 40-50 mL in sterile container
  - Synovial Fluid: Collected via arthrocentesis under sterile conditions; minimum 2-5 mL required
- Special Instructions/Patient Preparation:
  - No specific fasting or medication restrictions required
  - Notify physician of any bleeding disorders or anticoagulant therapy (aspirin, warfarin, direct oral anticoagulants) before procedure
  - Empty bladder before procedure (for peritoneal procedures)
  - Maintain sterile technique during collection to prevent contamination
  - Do NOT add formalin or other preservatives - specimen should be processed fresh when possible
  - Transport specimen immediately to laboratory (ideally within 2 hours) at room temperature in sterile container
  - Avoid refrigeration of most body fluids (except CSF which may be refrigerated if delay anticipated)
  - Inform laboratory if patient is on anti-TB therapy (may affect culture results)

How our test process works!