Tuberculosis

Testing site      

Alaska State Public Health Laboratory – Anchorage 

Anchorage Lab Request Form 

Diseases 

• TB 
• tuberculosis 

Organisms 

• Mycobacterium tuberculosis complex 
• Other Mycobacterium species
  • M. Avium/intracellulare complex
  • M. fortuitum
  • M. gordonae
  • etc.  

Test Method 

• Acid fast bacilli (AFB) smear 
• Liquid (MGIT) and solid (7H11) culture 
• MALDI-TOF MS identification and drug susceptibility (TB only) 
• TB nucleic acid amplification test (NAAT)  

Availability

Routine testing   

Specimen type 

• Pure isolate 
• Obtain material from the inflamed areas in the nasopharynx.  If the membranes are present and can be removed, swab from beneath the membrane 
• Throat, wound or nose swab 

Specimen collection instructions 

• Seal all specimens with Parafilm® (or similar) and refrigerate (except blood).  
• Do not use waxed containers or urine cups. 
• Swabs are not recommended for the isolation of Mycobacteria. 
• Ship samples on cool packs as UN3373 Biological substances, Category B, as soon as possible. 
• Specimens must be received in our laboratory within 10 days of collection. 

Sputum 

• Collect early morning specimens from a deep productive cough on three consecutive days, before the patient eats, drinks or takes medication. Use a separate collection tube for each day. 
• Rinse the patient’s mouth out with water prior to collecting the specimen.  
• Collect 5-10 mL sputum in sterile 50 mL screw-capped tubes containing sodium carbonate preservative. 

Blood 

• 10 mL of blood collected in SPS (yellow top) Isolator microbial tube 
• Store at room temperature. 

Bone Marrow  

• 10 mL of blood collected in SPS (yellow top) Isolator microbial tube 
• If isolator tubes are not available, use a sterile container with sterile saline. 

Bronchoalveolar lavage or Bronchial washing 

• Submit 5 mL in sterile container.  
• Avoid contaminating bronchoscope with tap water. 

Bronchial Brush/Brushing 

Submit in sterile container with sterile saline. 

Body Fluids (Pleural, peritoneal, synovial, pericardial, etc.) 

• Submit 10-15 mL in sterile 50 mL conical tubes.  
• Add sterile anticoagulant (SPS or heparin) to body fluids if necessary. 
• Do not use preservatives. 

CSF 

• Submit 2 mL in sterile container. 
• Gastric Lavage/Aspirate 
• Collect 5-10 mL of gastric washing in sterile 50 mL conical tube.  
• Adjust pH to neutral with 100 mg of sodium carbonate immediately following collection and note on requisition form. 

Stool 

• Submit samples in sterile 50 mL conical tubes. 
• Tissue, aspirate, bone, lymph nodes, biopsy, abscess contents 
• Submit samples in sterile 50 mL conical tubes.  
• Add sterile saline to cover specimen. 

Urine 

Collect first morning, clean catch, urine specimens on three consecutive days. Submit 40-50 mL of urine in a sterile 50 mL sterile crew capped conical tube. 

Storage/Transport  

Store refrigerated (except for blood).   

Ship with cool packs.  Ambient temperature shipping is acceptable. 

Specimens must be received at the Alaska State Public Health Laboratory – Anchorage within 10 days of collection. 

Storage and transport  

• Store refrigerated (except for blood).   
• Ship with cool packs.  Ambient temperature shipping is acceptable. 
• Specimens must be received at the Alaska State Public Health Laboratory – Anchorage within 10 days of collection. 

Ship to Alaska State Public Health Laboratory: Anchorage, ATTN: Clinical Microbiology 

Results  

• No AFB observed 
• 1+, 2+, 3+, or 4+ AFB observed 

A normal result is no AFB observed. 

TB Culture Result 

• No Mycobacterium species, including M. tuberculosis, isolated. 
• Mycobacterium tuberculosis complex by NAAT 
• Mycobacterium avium/intracellulare complex by MALDI-TOF 
• Other Mycobacterium identified by MALDI-TOF or Reference Lab 

A normal result is No Mycobacterium species, including M. tuberculosis, isolated.  

TB NAAT Result 

• Nucleic Acid Detected/Not Detected    

A normal result is nucleic acid not detected.  

TB NAAT Information 

The GeneXpert® Xpert® MTB/RIF Assay simultaneously identifies targeted nucleic acid sequences within the MTC and rifampin (RIF) resistance associated mutations of the rpoB gene in sputum.  

NAAT are performed on initial smear-positive specimens. Additionally, ASPHL will perform TB NAAT on smear-negative sputum specimens from patients considered to be TB suspects upon provider request and pre-approval from the Alaska Tuberculosis Program. These tests can provide a presumptive diagnosis, which can aid in the decision of whether to begin treatment before culture results are available. 

The Center for Disease Control and Prevention recommends NAAT be performed on at least one respiratory specimen from each patient with signs and symptoms of pulmonary TB for whom a diagnosis of TB is being considered but has not been established, and the test result would alter case management or TB control activities. 

Patient Criteria

• Patient must have signs and symptoms of pulmonary TB 
• Patient must be reported to the Alaska Tuberculosis Program as a suspect TB case (907-269-8000) 
• Patient must not have been diagnosed with TB or a nontuberculous mycobacterial infection or received treatment within the last 12 months 
• Refer to Tables 1, 2 & 3 for NAA testing algorithm and result interpretation. 

GeneXpert® Xpert® MTB/RIF Result Interpretation  

Gene Xpert® MTB/RIF and AFB Smear Combined Interpretation 

Possible scenarios include: 

• TB DNA present, visible cells, pending culture results 

• • AFB Smear: Positive 
  • MTB/RIF NAAT: Detected 
  • Interpretation: MTB target is detected within the sample. Use clinical judgment to determine whether to begin therapy while awaiting culture results. A positive NAAT does not necessarily indicate the presence of viable organisms. 

• Possible non-TB mycobacteria, pending culture results 

• • AFB Smear: Positive 
  • MTB/RIF NAAT: Not Detected 
  • Interpretation: MTB target is not detected within the sample. Use clinical judgment to determine whether to begin therapy while awaiting culture results. A patient is presumed to have an infection with nontuberculous mycobacteria, pending culture results. A negative MTB result on the Xpert MTB/RIF assay does not rule out pulmonary TB.  

• TB DNA detected, no visible cells, pending culture results 
  • AFB Smear: Negative 
  • MTB/RIF NAAT: Detected 
  • Interpretation: MTB target is detected within the sample. Use clinical judgment to determine whether to begin therapy while awaiting culture results. A positive NAAT does not necessarily indicate the presence of viable organisms. 
• No TB DNA, no visible cells, pending culture results 
  • AFB Smear: Negative 
  • MTB/RIF NAAT: Not Detected 
  • Interpretation: Use clinical judgment to determine whether to begin therapy while awaiting results of culture and other diagnostic tests. A negative MTB result on the Xpert MTB/RIF assay does not rule out pulmonary TB. 

Mycobacterium tuberculosis complex NAAT and culture results must be correlated with patient history to confirm as a case of TB infection. The GeneXpert® Xpert® MTB/RIF Assay detects the presence of a specific DNA sequence present in Mycobacterium tuberculosis complex (MTC), which includes:

• M. tuberculosis
• M. bovis
• M. bovis BCG
• M. africanum
• M. canettii
• M. microti
• M. caprae
• M. pinnipedii
• M. mungi
• M. orygis

Results from TB NAA tests are not intended to be used as the sole means for clinical diagnosis or patient management decisions. 

Susceptibility Result 

Performed on M. tuberculosis complex only.  First line drugs: Isoniazid, Rifampin, Ethambutol, and PZA (panel also includes Levofloxacin). 

Susceptible/Resistant 

A normal result is susceptible.  

Turnaround times  

AFB Smear: within 24 hours of specimen receipt 

TB Culture reports are released at various intervals: 

• Preliminary results: 3 weeks 
• Negative Culture: 6 weeks (minimum) 
• Positive Culture: As detected and confirmed 

TB NAAT:  GeneXpert® within 24 hours;  

Susceptibility: 1 to 2 weeks from identification 

Resources