Acid Fast Baccilli

Topics: Bacteria, Microbiology, Acid fast bacilli Pages: 6 (1176 words) Published: June 19, 2013
LABORATORY COLLECTION MANUAL Effective Date: 6/96

ACID FAST BACILLUS (AFB) SPECIMEN COLLECTION Page 1 of 4

I.

GENERAL PRINCIPLE Mycobacterial cultures are also known and ordered as cultures for TB or acid fast bacilli. Specimens submitted are either of pulmonary origin or of extra-pulmonary origin. The pulmonary type of specimen is almost always contaminated with normal respiratory flora with the exception of pleural biopsy or a transtracheal aspirate performed under aseptic conditions. Extra-pulmonary specimens that are considered contaminated are urine, stool, skin or soft tissue. Blood, bone marrow, suprapubic bladder aspirate, CSF, and other sterile body fluids, and aseptically collected tissue samples should be free of contamination.

II.

SPECIMEN COLLECTION A. General considerations 1. Currently all testing for acid-fast bacilli is performed by the State Health Department Laboratory in Austin. They offer more rapid turn around time on both stains and cultures than can be provided in house, as well as a more complete array of isolation media. Use sterile, leak proof disposable plastic containers for collection. Do not use wax containers as these can cause false positive smear results. Do not use any fixative or preservatives. Swabs are not recommended as a collection device for the isolation of mycobacteria. They are acceptable only if the specimen can not be obtained by any other means. A negative result from a swab specimen is not reliable. In general, the number of acid fast bacilli in a specimen is small. Early morning specimens are the specimens of choice for urine and sputum because the mycobacteria have had a chance to pool and concentrate, and so increase the chances of recovery. Always collect and submit the maximum volume possible of specimens normally considered sterile. Do not submit 24-hour collections, as they are likely to be diluted and contaminated. Collect specimens before antimicrobial therapy is started. Even a few days of therapy may kill or inhibit sufficient numbers of mycobacteria to prevent recovery on culture and so leave confirmation of disease in doubt. If a specimen is submitted after therapy has been initiated, note on the request. Avoid contamination of the specimen with tap water, as environmental mycobacteria exist and their recovery by smear or culture can cause confusion for the patient diagnosis. Stains for acid fast bacilli can be performed on specimens collected as detailed below. The only exception is urine, and AFB staining is not performed by the State Health Department Laboratory for this specimen.

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LABORATORY COLLECTION MANUAL Effective Date: 6/96

ACID FAST BACILLUS (AFB) SPECIMEN COLLECTION Page 2 of 4

B. 1. 2.

Aspirated body fluid or abscess Cleanse skin with alcohol before aspirating sample. Submit as much volume as possible in a sterile container; or as second choice, in the syringe with needle removed and syringe recapped with syringe cap. (Use a recapping device).

C.

Blood or bone marrow 1. 2. Collected as routine for blood culture or bone marrow. Place sample in an Isolator blood culture collection tube and mix vigorously. A Vacutainer tube with SPS (yellow top) is also acceptable. SPS is the preferred anticoagulant, as it enhances mycobacterial growth. Coagulated blood, or blood collected with EDTA as the anticoagulant are unacceptable.

3. D. Bone 1. 2. E.

Place in a sterile container without fixative or preservative. Specimen submitted in formalin is unacceptable.

Bronchial washing 1. 2. Avoid contaminating the bronchoscope with tap water. Submit at least 5 ml of washings in a sterile container.

F.

CSF 1. 2. Submit the maximum volume attainable. Submission of less than 2 ml will generate a comment from TDH of "inadequate volume".

G.

Skin lesions (wounds) 1. 2. 3. Collect biopsy specimen...
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