Identification of Acid Fast Bacilli
Test Code
AFB4
Description
This test is used for identification of acid fast bacilli (AFB) or partially acid fast organisms. Identification is performed to the greatest extent possible, which is usually to the species level but can be to the subspecies level for some organisms (e.g. Mycobacterium abscessus subsp. abscessus). See below for the different platforms, assays, and techniques that may be employed.
This test is ordered for pure isolates sent to the laboratory for identification (e.g. AFID). It does not need to be ordered separately for clinical samples that require organism identification since it is automatically included in those tests (e.g. AFB1 and AFB3).
Collect
Isolates of mycobacteria or partially acid fast organisms in solid media such as Middlebrook slant (7H10 or 7H11), Lowenstein-Jensen medium slant, or in broth (7H9, MGIT, MP BACT/Alert, VersaTrek).
Specimen volume: Lab must receive visible growth of isolate on solid media or an isolate in broth media (≥3 mL).
Unacceptable Conditions
- Cultures received with incomplete identifiers.
- Mixed cultures; Note that prior to rejection, attempts will be made to isolate the organisms. A reisolation charge will be applied in these cases.
- Cultures containing mold.
- Solid media with insufficient growth.
- Liquid media with <2 mL.
- Leaking specimens.
Storage Transport Temp
Transport or mail isolates at ambient temperature. For nontuberculous mycobacteria (NTM), follow IATA/ DOT category B and for M. tuberculosis complex isolates, follow IATA/DOT category A requirements for shipping biological materials.
Performed
Dependent on method used; see methodology section.
Methodology
| Method | Usage | Internal order code applied | Days performed |
|---|---|---|---|
| PCR/MALDI-TOF mass spectrometry | Primary assay used on isolates for identification of M. tuberculosis complex, M. avium complex, M.kansasii, and subspeciation of M. abscessus. | MASID | Tu-Sat |
| Line probe assay | Typically used for speciation of M. tuberculosis complex, M. avium complex, and subspeciation of M. abscessus. | NTMID or MTB7 | Tu-Sat |
| Sequencing | Typically used for speciation of uncommon mycobacteria, confirmation of M. intracellulare, or aerobic actinomycetes. | 16S or RPOB | Once a week |
Turnaround Time
Identification results are reported within 3 days to 2 weeks depending on which method is used.
Department
Infectious Disease Laboratory, Mycobacteriology
Synonyms
Line probe assays, Hain, sequencing, identification, reverse hybridization assay
Related Tests
AFB1, AFB3, VETCX, ENVCX
Interpretation
Organisms growing in pure cultures are identified to the species or subspecies level whenever possible or appropriate.
CPT Code
Below are different test methods used for identification of various types of AFB and partially acid fast organisms. Only the relevant test methods will be performed and charged for the organism recovered or sent to the lab.
| Test | Method | CPT Code | Billing Code | When is this applied? |
|---|---|---|---|---|
| AFB identification | PCR/MALDI-TOF Mass spectrometry | 87798 x 9 | MASID (1st organism), MASI2 (2nd organism), MASI3 (3rd organism) |
If an appropriate organism is recovered. |
| Line probe assay | 87798 x 7 | NTMID (1st organism), NTMD2 (2nd organism), NTMD3 (3rd organism) |
If an appropriate organism is recovered. | |
| MTB identification | Line probe assay | 87556 x 6 | MTB7T | If an appropriate organism is recovered. |
| rpoB identification | Sanger Sequencing | 87153 | RPOB | If an appropriate organism is recovered. |
| 16S Identification | Sequencing | 87153 | 16S | If the appropriate organism is recovered. |
| Isolation of AFB from contaminants | Culture | 87116 | ISOIP | Reisolation for mixed or contaminated isolates received from facility. |