Advanced Diagnostic Laboratories

Smear, Culture, and Identification of M. tuberculosis complex

Test Code

VETCX

Description

This test includes AFB smear, culture, and identification of Mycobacterium tuberculosis complex from a clinical specimen. Nontuberculous mycobacteria and other partially acid fast organisms are not identified.

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 M.tuberculosis complex is identified and speciated to the greatest extent possible.

This test is typically performed for veterinary purposes (e.g. elephants, non-human primates and other animals where M. tuberculosis complex is suspected), but may be used in human cases after discussion with the laboratory.

Nucleic acid amplification testing for M. tuberculosis is not performed. If a complete workup of all AFB is needed, order AFB1. If workup of NTM in particular is desired, order AFB3.

Collect

Specimen	Preferred Volume	Unacceptable Conditions	Collection Container	Total Stability Time, including transport
Elephant Trunk Washes	5-10 mL 3-5 mL is accepted, but a disclaimer of low sample volume is added.	<1 mL	Sterile, leak-proof container.	7 days refrigerated; 72 hours ambient.
Sputum (expectorated or induced)	5-10 mL	<3 mL	Sterile, leak-proof container.
Lower respiratory tract (e.g., bronchoalveolar lavage (BAL))	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 (e.g., pericardial, synovial, pleural etc.)	2-4 mL	<2 mL	Sterile, leak-proof container
Cerebrospinal fluid (CSF)	2-4 mL	<2 mL or refrigerated/frozen CSF.	Sterile, leak-proof container	72 hours ambient. This should not be refrigerated.
Fresh tissue	1-2 g	<1g or tissue submitted on a dry swab or fixed in formalin or other preservatives.	Sterile, leak-proof container 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 collection green (heparin) or yellow (SPS) tube.
Gastric lavage or wash	10 mL	<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	<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.	7 days refrigerated.

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

Stability

See table under Collection Requirements

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. Molecular testing is performed for Mycobacterium tuberculosis complex isolates to differentiate M. tuberculosis, M. africanum, M. bovis and M. bovis BCG.

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.
Identification is reported within 3 days to 2 weeks, depending on the method(s) used.

Department

Infectious Disease Laboratory, Mycobacteriology

Synonyms

specimen, animal, Vet, VETCX, elephant, MTBC, Mycobacterium tuberculosis culture

Study Offerings

CAP/CLIA

Reference Interval

Negative for acid fast bacilli

Interpretation

Test	Interpretations
AFB Smear	Fluorochrome stain read at 400X No AFB found Doubtful: Repeat specimen recommended. 1 to 2 AFB seen/ 70 fields observed. 1+= 2-18 AFB/ 50 fields observed. 2+= 4-36 AFB/ 10 fields observed. 3+= 4-36 AFB/ field observed. 4+= >36 AFB/ field observed.
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).
AFB Identification	Organisms are identified to the species level where possible.

CPT Code

Test	Method	CPT Code	Billing Code	When is this applied?
AFB Smear	Fluorochrome 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
MTB Identification	Line Probe	87556	MTB7T	If an appropriate organism is recovered