Tuberculosis (TB) is one of the world's deadliest diseases1:

  • One fourth of the world's population is infected with TB.1
  • In 2020:
    • About 10 million people around the world became sick with TB disease.1
    • There were 1.5 million TB-related deaths worldwide.1
    • A total of 7,860 new cases of TB were reported in the United States.1
  • TB diagnostic testing is important; once an infection is detected it is treatable and curable.
  • TB drug resistance remains a serious issue. Susceptibility testing helps patients receive the most effective treatment.

Acid-Fast Bacillus (AFB) Culture

ARUP’s AFB lab performs testing seven days a week isolating, identifying, and performing susceptibility on most mycobacteria species. We use a combination of MALDI-TOF, PCR, and 16S rRNA sequencing to obtain species-level identification using known quality controlled databases.

Run Times

ARUP processes several runs per day, every day of the week, and report stains as soon as completed.

Result Reporting

Preliminary report and AFB stain results within 24 hours:

“Specimen received and in progress. Positive culture reports are called as soon as detected. Final report to follow in seven to eight weeks.”

Positive stain results are called to clients.

AFB Identification Methods

  • Cultures are set up in MGIT broth and solid media and are continuously monitored.
  • Positive results are called and reported as soon as detected.
  • MALDI-TOF, PCR, and 16S rRNA sequencing are all performed daily with fresh subcultures.
  • M. tuberculosis complex positive organisms will be identified to the species level by PCR.
  • Positive culture preliminary reports are updated with the progress of the identification.
  • Positive cultures are reported as a final report after the organism has grown on solid media and the organism morphology is consistent with the initial identification.

AFB Susceptibility Testing

Susceptibility testing will be performed for all initial M. tuberculosis complex isolates and rapidly growing mycobacteria. When Acid-Fast Bacillus (AFB) Identification with Reflex to Susceptibility (ARUP Test Code: 0060997) is ordered, susceptibility testing is performed on all primary isolates of M. tuberculosis complex and clinically significant non-TB mycobacteria, regardless of the source. Susceptibility testing is performed automatically when the following organisms are detected:

M. tuberculosis complex, M. kansasii, M. avium-intracellulare, M. abscessus, M. chelonae, M. immunogenum, M. fortuitum
complex and M. mucogenicum

For organisms outside of the list above, the physician should decide if susceptibility testing is appropriate. We will proceed with susceptibility testing at the physician's request for these isolates.

Unless ARUP receives a specific request, susceptibility testing will not be performed on isolates received within 90 days of a previous specimen, even if the isolates are from different sources.

Antimicrobials Tested and Reported

  • M. tuberculosis complex: Ethambutol, isoniazid (INH), pyrazinamide (PZA), and rifampin. We send isolates to National Jewish Health for all secondary drug testing as requested by physician.
  • M. kansasii: Rifampin and clarithromycin. Rifampin-susceptible isolates are also susceptible to rifabutin. If the isolate is rifampin-resistant, the following secondary drugs will also be reported: Amikacin, ciprofloxacin, linezolid, moxifloxacin, rifabutin, streptomycin, and trimethoprim/sulfamethoxazole.
  • M. avium-intracellulare complex: Amikacin, clarithromycin, linezolid, and moxifloxacin. Clarithromycin results predict azithromycin. Because MIC results do not predict clinical response and may be misleading, rifampin, rifabutin, and ethambutol MICs are not tested.
  • Rapid growers (M. abscessus, M. chelonae, M. immunogenum, M. fortuitum complex, and M. mucogenicum): Amikacin, cefoxitin, ciprofloxacin, clarithromycin, doxycycline, imipenem, linezolid, moxifloxacin, tigecycline, and trimethoprim/sulfamethoxazole. Tobramycin reported on M. chelonae. Extended 14-day incubation is performed on isolates initially susceptible to clarithromycin to detect erm(41)-dependent inducible macrolide resistance except in Mycobacterium species with a nonfunctional erm(41) gene.
  • Other slow growing nontuberculosis mycobacteria (NTM): Amikacin, ciprofloxacin, clarithromycin, doxycycline, linezolid,  moxifloxacin, rifabutin, rifampin, streptomycin, and trimethoprim/sulfamethoxazole

Test Information

Test NumberTest NameRecommended Use and Advantage
0060217Antimicrobial Susceptibility, AFB/MycobacteriaOrder for SUSCEPTIBILITY of clinically significant isolates of M. tuberculosis complex (MTBC), M. kansasii, M. avium-intracellulare complex, M. fortuitum complex, M. abscessus complex, M chelonae, M immunogenum, and any isolate from a significant source.
0060347Antimicrobial Susceptibility, AFB/Mycobacterium tuberculosis Primary PanelOrder when phenotypic drug susceptibility testing is required for M. tuberculosis complex treatment.
0060999Acid-Fast Bacillus (AFB) IdentificationOrder to identify mycobacterial isolates, including requests for speciation within the M. tuberculosis complex.
0060997Acid-Fast Bacillus (AFB) Identification with Reflex to SusceptibilityOrder to identify mycobacterial isolates and perform susceptibility testing.
0060152Acid-Fast Bacillus (AFB) Culture and AFB StainOrder as a gold standard test for diagnosing the presence of mycobacteria organisms.
0060738Acid-Fast Bacillus (AFB) Culture and AFB Stain with Reflex to Mycobacterium tuberculosis Complex Detection and Rifampin Resistance by PCROrder for a comprehensive panel that includes acid-fast bacillus culture and stain. Positive smears reflex to PCR amplification of M. tuberculosis complex species and rifampin resistance.
2010775Mycobacterium tuberculosis Complex Detection and Rifampin Resistance by PCROrder for a panel that includes PCR testing to detect M. tuberculosis complex isolates and determine possible resistance to rifampin treatment. This test may be ordered for client-processed specimens. Refer to the ARUP test directory for specimen requirements.
0060060Blood culture, Acid Fast BacillusOrder to identify acid-fast bacteria in blood or bone marrow specimens. Cultures are monitored continually. Identification and susceptibility testing is performed on positive cultures at an additional charge.
0060024Blood culture, AFB and FungalOrder to identify acid-fast bacteria and fungi in blood or bone marrow specimens. Cultures are monitored continually. Identification and susceptibility testing is performed on positive cultures at an additional charge.

Additional Resources

References

1. World Health Organization. Tuberculosis. https://www.who.int/news-room/fact-sheets/detail/tuberculosis (accessed on September 19, 2022).