Nucleic Acid Amplification Test (NAAT) for M. tuberculosis from clinical specimens
Test Code
NAAT or AFB2c (Old code: AFB2)
Description
This test detects M. tuberculosis complex and rifampin resistance from a specimen using nucleic acid amplification testing (NAAT). The NAAT is performed to rapidly rule-in or rule-out M. tuberculosis complex infection, identify resistance to rifampin, and triage potentially infected patients appropriately for airborne isolation. It should not be used as a test of cure.
The Centers for Disease Control and Prevention (CDC) recommends that NAAT should 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 yet been established, and for whom the test result would alter case management or TB control activities.
This test is automatically included as part of AFB1, the full AFB workup. It can be ordered separately or added-on to another test.
Collect
| Specimen | Volume | Method | Total stability time including transport |
|---|---|---|---|
| Sputum (expectorated or induced) | 2 mL | Real-time PCR | 7 days refrigerated; 72 hours ambient. |
| Lower respiratory tract specimen (e.g. bronchoalveolar lavage, bronchial washes etc.) | 2 mL | Real-time PCR | |
| Body fluids (pericardial, synovial, pleural etc.) | 2 mL | Line Probe | |
| Cerebrospinal fluid (CSF) | 2 mL | Real-time PCR | 72 hours ambient. This source should not be refrigerated. |
| Fresh Tissue | 1 g | Line Probe | |
| FFPE Tissue | 1 g | Line Probe | |
| Gastric lavage or wash | 2 mL | Line Probe | |
| Urine | 2 mL | Real-time PCR | 7 days refrigerated. |
Unacceptable Conditions
- Specimen received with <1.5 mL volume.
- Saliva
- Frozen specimen
- Swabs
- Blood specimen
- Stool specimen
Notes
The Centers for Disease Control and Prevention (CDC) recommends that NAAT should 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 yet been established, and for whom the test result would alter case management or TB control activities.
TB NAAT is not performed on swabs, stool, or blood specimens.
Performed
Typically all days.
Methodology
Real-time PCR or line probe assay
Turnaround Time
Results are typically reported in less than a day, but may be 1-3 days for non sputum sources.
Department
Infectious Disease Laboratory, Mycobacteriology
Synonyms
Mycobacterial PCR, Tuberculosis PCR , MDR, TB PCR, MTB PCR
Related Tests
This test is a component of AFB1; MTB4 is a genotypic assay to detect resistance markers to first line drugs.
Reference Interval
M. tuberculosis complex not detected.
Interpretation
- M. tuberculosis complex may be Detected, Not Detected, or Indeterminate.
- Rifampin resistance may be Detected, Not Detected or Indeterminate. In cases where the line probe assay is used instead of real-time PCR, rifampin resistance is Present, Not Present, or Indeterminate. Isoniazid may also be reported.
CPT Code
| Test | Method | CPT code | Billing code | When is this applied? |
|---|---|---|---|---|
| NAAT or AFB2C | Real-time PCR | 87556 | AFB2C | On sources where real-time PCR can be used. See "Method" under Collection Requirements. |
| NAAT or MTB4 | Line Probe | 87798 x 2 | MTB4S | On sources where the line probe can be used. See "Method" under Collection Requirements. |