Lab Dept:

Microbiology/Virology

Test Name:

AFB SMEAR, DIRECT

General Information

Lab Order Codes:

AFBD

Synonyms:

Acid-Fast Stain; TB Stain; Atypical Mycobacterium Smear; Mycobacterium Smear

CPT Codes:

87206 – Smear, primary source with interpretation; fluorescent and/or acid fast stain for bacteria, fungi, parasites, viruses or cell types

Test Includes:

Screen of unconcentrated material for acid-fast bacilli performed at Children’s Hospitals and Clinics of MN. Specimen will be referred to the Minnesota Department of Health for acid-fast culture and concentrated smear. All positive results are reported immediately by phone to the physician or patient’s nurse.

Logistics

Lab Testing Sections:

Microbiology

Phone Numbers:

MIN: 612-813-5866

STP: 651-220-6555

Test Availability:

Daily, 0700 - 1530

Turnaround Time:

24 hours

Special Instructions:

● For diagnosis, an acid-fast culture must also be ordered.
● Specific site and date/time of collection are required for specimen processing.
● Swabs are unacceptable for Direct AFB smear exam.

Specimen

Specimen Type:

The appropriate specimen for an acid-fast smear is the same as for culture; except when the specimen is submitted on a swab, or is a body fluid, CSF or urine. Because of the acellular nature of these specimens, they must be concentrated and cannot be used.

Specimens may include aspirates (abscess), bronchial wash, gastric aspiration, skin, sputum, tissue, and stool.

Refer to AFB Culture for details.

Container:

Sterile container

Collection:

Refer to AFB Culture for collection information.

Transport/Storage:

Transport to the laboratory promptly. Refrigerate if there is a delay >2 hours.

Sample Rejection:

Specimen with a transit time exceeding 2 hours after collection; specimen not submitted in appropriate transport container; improperly labeled specimen; 24 hour urines; 24 hour sputum collections; insufficient volume; external contamination. If an unacceptable specimen is received, the physician or nursing station will be notified and another specimen requested before discarding the specimen.

Interpretive

Reference Range:

No acid-fast organisms seen

Critical Values:

Positive AFB smears will be called to the physician or patient’s nurse.

Limitations:

Cultures are more sensitive than smears, therefore, negative acid-fast smears do not exclude a diagnosis of mycobacterial disease. A positive acid-fast smear without concentration requires a very active infection. Acid-fast stains are not specific for M. tuberculosis; other species in the genus Mycobacterium will stain acid-fast, and other organisms will occasionally stain acid-fast (eg, Nocardia sp, Legionella micdadei, Rhodococcus equi). Immunocompromised individuals (eg, those who are HIV positive) may have infection by organisms of the Mycobacterium avium-intracellulare complex (MAC). Definitive identification can only be accomplished by culture and subsequent phenotypic or genotypic characterization. Occasional strains of rapidly growing mycobacteria may not be acid-fast by fluorochrome stains.

Methodology:

Auramine-rhodamine stain

References:

Cook, JH, and M Pezzlo (1992). Specimen receipt and accessioning. Section 1. Aerobic bacteriology, 1.2.1-4. In HD Isenberg (ed) Clinical Microbiology Procedures Handbook. American Society for Microbiology, Washington DC

Miller, J Michael (1999) A Guide To Specimen Management in Clinical Microbiology, American Society for Microbiology, Washington DC

Miller, J Michael, and HT Holmes (1999) Specimen Collection, Transport, and Storage In PR Murray et al, (ed), Manual of Clinical Microbiology, 7^th edition, American Society for Microbiology, Washington DC, pp 33-104

Updates:

10/15/12: Removed notification of Infection Prevention for positive results. Swabs are no longer accepted for this testing.