Smear and Culture (only) of Acid Fast Bacilli
Test Code
AFB7
Description
This test includes AFB smear and culture from a clinical specimen. Growth of acid-fast bacilli is reported but full identification is not performed.
The AFB smear is a direct fluorescent stain from the specimen and can be used to quickly establish the presence of mycobacteria. The AFB culture is the inoculation of a clinical specimen onto multiple media types followed by monitoring for six weeks. Growth of any AFB (i.e. mycobacteria) or partially acid fast organisms (e.g. aerobic actinomycetes) is reported.
This test order is typically a component of other workup algorithms (e.g. AFB1 and AFB3). It is used on its own only in specific circumstances and after discussion with the laboratory.
Collect
| Specimen | Preferred Volume | Unacceptable Volume | Collection Container | Total stability time, including transport |
|---|---|---|---|---|
| Sputum (expectorated or induced) | 5-10 mL | <3 mL | Sterile, leak-proof container. | 7 days refrigerated; 72 hours ambient. |
| Lower respiratory tract (e.g. bronchoalveolar lavage, bronchial washes etc.) | 5-10 mL | <3 mL | Collect washing and aspirates in a sputum trap. Place brushes in a sterile, leak-proof container with up to 5 mL sterile non-bacteriostatic saline. | |
| Body Fluids (pericardial, synovial, pleural etc.) | 2-4 mL | <2 mL | Sterile, leak-proof container. | |
| Cerebrospinal fluid (CSF) | 2-4 mL | <2 mL refrigerated/frozen CSF. | Sterile, leak-proof container. | 72 hours ambient. This source should not be refrigerated. |
| Fresh Tissue | 1-2 g | <1 g or tissue submitted on a dry swab or fixed in formalin or other preservatives. | Sterile, leak-proof container with tissue submerged in sterile non-bacteriostatic saline. | |
| Blood | 5-10 mL | <5 mL or blood collected in a red-top, EDTA (purple-top) or ACD (yellow-top) tubes. | Sterile, leak-proof blood collection green (heparin) or yellow (SPS) top tube. | |
| Gastric lavage or wash | 10 mL required | <10 mL or a specimen that has not been neutralized within 1 hour of collection. | Sterile, leak-proof container. Neutralize specimen within 4 hours of collection with 100 mg of sodium carbonate. | |
| Urine | 5-10 mL required | <3 mL, Pooled urine specimen, or a urine specimen that has been mixed with preservatives. | Sterile, leak-proof container. | 7 days refrigerated. |
| Stool | 1-2 g | <1 g or a stool specimen in PVA, formalin, or other preservative, rectal swabs. | Sterile, leak-proof container. |
Unacceptable Conditions
- Samples collected in wax containers are not acceptable. Wax containers may produce false-positive smear results.
- Swabs are not recommended for the isolation of mycobacteria, since they provide limited material and the hydrophobicity of the mycobacterial cell envelop often compromises a transfer from the swabs onto solid media or into broth media.
- Specimen received in the lab 14 days post-collection
Notes
- Stool cultures for mycobacteria are not encouraged.
- AFB smear is not performed for urine, stool, or blood.
Performed
Typically all days.
Methodology
When appropriate, specimens are processed using a standard digestion/decontamination procedure. An acid fast smear is performed from the processed specimen using a florescent auramine stain. Specimens are cultured on three solid and one liquid media then incubated for 6 weeks.
Turnaround Time
- AFB Smear reported within 24 hours. Note that AFB smears are not performed for urine, stool, or blood.
- The final report for the AFB culture is issued at 6 weeks. Solid media cultures are read at 1, 3, and 6 weeks. Liquid media cultures are continuously monitored. Positive cultures are reported at the time of positivity and negative cultures are reported at 1, 3, and 6 weeks. In some cases, media may be incubated for up to 8 weeks and if positive, a supplemental report will be issued.
Department
Infectious Disease Laboratory, Mycobacteriology
Synonyms
AFB7, mycobacterial smear and culture
Reference Interval
Negative for acid fast bacilli.
Interpretation
| Test | Interpretations |
|---|---|
| AFB Smear | Fluorochrome stain read at 400X
|
| AFB Culture | Negative cultures are reported as negative for growth Positive cultures are reported as organisms recovered with a colony count where possible (CFU/mL) |
CPT Code
This is a test algorithm. When it is ordered, smear and culture are typically performed.
| Test | Method | CPT code | Billing code | When will this be applied? |
|---|---|---|---|---|
| AFB Smear | Fluorchrome stain | 87206 | CXAFB1 | All samples, except blood, stool and urine |
| AFB Culture | Specimen processing | 87015 | CXAFB2 | All samples |
| AFB Culture and Presumptive ID | Culture | 87116 | CXAFB3 | All samples |