Mycobacterium tuberculosis (MTB) complex NAAT

TEST DESCRIPTION

Detection of Mycobacterium tuberculosis (MTB) complex DNA and rifampin resistance by nucleic acid amplification test (NAAT).   This test is a qualitative, real-time polymerase chain reaction (PCR) method used for detecting MTB complex in acid-fast bacilli (AFB) smear-positive and smear-negative respiratory specimens. 

 Limitations include:

• The test is only validated for sputum and bronchial washings/aspirate specimens and for AFB-positive culture isolates.
• The test is not indicated for use with specimens from patients being treated with antituberculosis agents to determine bacteriologic cure or to monitor response to such therapy. 
• Specimens that are grossly bloody should not be tested; blood may cause nonspecific positivity.
• A positive test does not necessarily indicate the presence of viable organisms.

Methodology

PCR

Reference range

Not detected

TEST FREQUENCY & RESULT AVAILABILITY

Performed daily. Results are typically available one business day after specimen receipt.

ACCEPTABLE SPECIMEN TYPES AND COLLECTION

• Sputum, including induced sputum: minimum volume of 1 ml
• Bronchial washings/aspirate: minimum volume of 1 ml
• Note: Non-validated specimens (e.g., CSF, smear-positive non-respiratory specimen) may be tested for surveillance purposes, but the laboratory report will not include an MTB complex NAAT result.
• Detailed collection instructions appear below

SPECIMEN STORAGE

Store in a sterile container at refrigerated temperature (2–8 °C/36–46 °F) for up to 72 hours. 

SPECIMEN TRANSPORT

Shipping conditions should follow the temperature and time requirements outlined above.

REJECTION CRITERIA

• Any specimen older than 72 hours from collection
• Volume less than 1 mL (approximately a rounded teaspoon)
• Specimens that have not been stored or transported refrigerated (2–8 ºC)
• Any dried-out specimen
• Specimen container not labeled
• Specimen container has leaked or is not sealed properly

CODES

CPT: 87564

LOINC: 38379-4

Test code: 3530

TEST FEE

Refer to the current fee schedule.

DETAILED SPECIMEN COLLECTION INSTRUCTIONS

1. Sputum
   1. Collection instructions
      1. Rinse throat and mouth with water (do not brush teeth or use mouthwash).
      2. Cough very deeply and collect between 5 and 10 mL of sputum (about an inch high) into the specimen tube. Sputum is the mucus material from inside the lungs. Do not collect saliva or nasal discharge.
      3. Tightly screw the cap onto the tube. If the cap is crooked, your specimen may leak and will be rejected.
      4. Label the tube with the patient’s name, date of birth, date collected and time collected.
   2. Sputum both expectorated and induced is the principal specimen obtained for the diagnosis of pulmonary tuberculosis.
   3. Sputum specimens should be collected in the early morning. 
   4. Optimal collection is 5-10 ml of sputum in a clean, sterile, leak-proof, screw-cap container. 
   5. Minimum specimen volume is 1 ml.
   6. Saliva specimens are acceptable since saliva has been demonstrated to have clinical utility in diagnosing pulmonary tuberculosis.
   7. Specimens may not be pooled over time.
2. Bronchoalveolar lavage, bronchial washing, aspirate, or brushing
   1. These specimens are collected in a clinical setting, and appropriate for patients unable to produce sputum.
   2. The clinician should collect as much material as is reasonably possible. Although there is no minimum volume, the recommended volume is ≥3 ml.