Acid-fast bacilli (mycobacteria) culture

TEST DESCRIPTION

Detection and isolation of acid-fast bacilli (AFB) from primary specimens by culture in liquid and solid media. Culture media are monitored for six weeks, and suspicious colonies are stained by modified Kinyoun stain to confirm acid-fastness. A positive finding indicates the presence of a mycobacteria species. Culture is more sensitive in detecting Mycobacterium species than both smear and nucleic acid amplification test (NAAT). AFB-positive cultures are reflexed to MALDI-TOF for identification.

Methodology

Liquid and solid media culture

Reference range

No growth at 4 and 6 weeks

TEST FREQUENCY & RESULT AVAILABILITY

Performed daily. Preliminary and final reports for negative specimens are issued at 4 and 6 weeks, respectively. Positive findings are reported when acid-fast bacilli are detected; final identification may exceed 6 weeks.

ACCEPTABLE SPECIMEN TYPES AND COLLECTION

• Primary specimens including:
  1. Sputum: minimum volume of 1 ml
  2. Bronchoalveolar lavage, washing, aspirate, or brushing; recommended volume of ≥3 ml
  3. Gastric lavage: minimum volume of 5 ml
  4. CSF: minimum volume of 1 ml
  5. Body fluids: recommended volume of ≥3 ml
  6. Urine: minimum volume of 40 ml
  7. Stool: minimum amount of ≥1 g
  8. Tissue and biopsy samples: recommended amount of ≥20 µg
• Detailed collection instructions appear below

SPECIMEN STORAGE

Store in a sterile container at ambient temperature for up to 1 hour and at refrigerated temperature (2–8 °C/36–46 °F) for up to 7 days. Gastric lavage specimens must be received by the laboratory within 3 hours of collection. 

SPECIMEN TRANSPORT

Shipping conditions should follow the temperature and time requirements outlined above.

REJECTION CRITERIA

• Any specimen older than 7 days from collection
• Specimens that have not been stored or transported refrigerated (2–8 ºC)
• Specimens not stored refrigerated within 1 hour after collection
• Any dried-out specimen
• Unlabeled specimens, improperly labeled specimens, or specimens where name on requisition does not match name on specimen
• Pooled sputum or urine specimens
• Low-volume specimens are to be rejected and resulted as unsatisfactory. Low-volume specimens are:
  1. Sputum <1 ml
  2. Gastric lavage <5 ml
  3. Urine <40 ml
  4. CSF <1 ml
  5. Stool <1 gram

CODES

CPT: 87116
LOINC: 543-9
Test code: 3545

TEST FEE

Refer to the current fee schedule.

DETAILED SPECIMEN COLLECTION INSTRUCTIONS

1. Sputum
   1. Collection instructions
      1. Rinse throat and mouth with water (do not brush teeth or use mouthwash).
      2. Cough very deeply and collect between 5 and 10 mL of sputum (about an inch high) into the specimen tube. Sputum is the mucus material from inside the lungs. Do not collect saliva or nasal discharge.
      3. Tightly screw the cap onto the tube. If the cap is crooked, your specimen may leak and will be rejected.
      4. Label the tube with the patient’s name, date of birth, date collected and time collected.
   2. Sputum both expectorated and induced is the principal specimen obtained for the diagnosis of pulmonary tuberculosis.
   3. Sputum specimens should be collected in the early morning. Patients suspected of having tuberculosis should submit a minimum of 3 consecutive specimens at least 8 hours, but no more than 1 day, apart. 
   4. Optimal collection is 5-10 ml of sputum in a clean, sterile, leak-proof, screw-cap container. 
   5. Minimum specimen volume is 1 ml.
   6. Saliva specimens are acceptable since saliva has been demonstrated to have clinical utility in diagnosing pulmonary tuberculosis.
   7. Specimens may not be pooled over time.
2. Bronchoalveolar lavage, bronchial washing, aspirate, or brushing
   1. These specimens are collected in a clinical setting, and appropriate for patients unable to produce sputum.
   2. The clinician should collect as much material as is reasonably possible. Although there is no minimum volume, the recommended volume is ≥3 ml.
3. Gastric lavage
   1. Specimens are collected in a clinical setting and should be processed within 4 hours of collection. If they cannot be processed within 4 hours, they should be neutralized with 100 mg sodium carbonate.
   2. Minimum specimen volume is 5 ml.
4. CSF
   1. CSF is collected in a clinical setting. The minimum specimen volume for CSF is 1 ml.
5. Body fluids other than CSF
   1. Pleural, pericardial, synovial, ascitic, and pus fluids are collected in a clinical setting. As much volume as possible should be collected into a sterile container.
   2. Although there is no minimum volume, the recommended volume for body fluid specimens is ≥3 ml.
6. Urine 
   1. Collect a minimum of 40 ml first morning urine obtained by midstream clean catch in a sterile cup without preservative. Specimens should be collected on 3 consecutive days.
7. Stool
   1. Usually only indicated in immunocompromised patients.
   2. Collect ≥1 gram in a sterile, wax-free, disposable container.
8. Tissue and biopsy samples
   1. Specimens are collected in a clinical setting, placed in a sterile container with a small amount of sterile saline or buffer to prevent drying.
   2. The clinician should collect as much material as is reasonably possible. Although there is no minimum amount, the recommended amount is ≥20 μg.