Test Overview
BD MGIT, Culture
AFB Culture, sputum (BAFB)
AFB (Acid-Fast Bacilli) culture of sputum is used for the detection and isolation of mycobacteria, most importnatly the Mycobacerium tuberculosis complex, as well as nontuberculosis mycobacteria (NTM) such as Mycobacterium avium complex and rapid growers such as M. abscessus. It is indicated in patients with suspected pulmonary mycobaterial infection, particularly those with chronic cough, hemoptysis, weight loss, fever, or imaging findings such as cavitary or nodular lung disease. The test is also appropriate for evaluating immunocompromised patients with compatible respiratiry symptoms and for monitoring microbiologic response to therapy in known tuberculosis cases.
Culture remains the gold standard for diagnosis because it enables definitive organism identification and antimicrobial susceptibility testing, although results may take 1-3 weeks for rapid-growing species and up to 6-8 weeks for slow-growing organisms. AFB culture is routinely performed in conjunction with AFB smear microscopy, with smear results reported within 24 hours of specimen processing. Nucleic Acid Amplification Testing (NAAT) for detection of M.tuberculosis complex is only performed when AFB smear positivity and requested by clinician and will incur an additional charge.
AFB Culture, sputum, TB Diagnostic Evaluation (TBSD)
This test is only for use within the Michigan Medicine TB Evaluation Order Set, specifically designed for evaluation of Adult Inpatients with signs and symptoms of pulmonary tuberculosis, for whom a diagnosis of tuberculosis is being considered but has not yet been established, and for whom the test result would alter management or tuberculosis control activities. In addition to AFB Smear and Culture, NAAT for rapid detection of M. tuberculosis complex will be routinely performed on one of the three sputum specimens submitted for diagnostic evaluation regardless of smear positivity. NAAT provides important diagnostic value in patients with suspected pulmonary tuberculosis when the AFB smear is negative. Because smear microscopy requires a relativly high bacillary burden for detection, a negative smear does not exclude infection. NAAT can detect Mycobacterium tuberculosis complex DNA at much lower organism loads, allowing for earlier diagnosis is paucibacillary disease.
No growth of mycobacteria
* Reference ranges may change over time. Please refer to the original patient report when evaluating results.
Sensitivity is dependent upon organism burden and specimen quality. Improperly collected sputum (e.g.,saliva rather than deep respiratory secretions) further reduces diagnostic yield. In addition, prior or ongoing antimicrobial therapy - including agents with antimycobacterial activity - can supress growth and decrease culture positivity. While more sensitive than AFB smear microscopy, culture may still be negative in cases of low organism burdn. A positive culture with nontuberculosis mycobacteria (NTM) does not necessarily indicate disease, as these organisms may represent colonization or environmental contamination. Clinical correlation, repeat isolation, and supporting radiographic and clinical findings are required for interpretation.
Test Details
Preliminary results on all cultures are reported in 12-24 hours. Negative cultures are reported after 6 weeks.
- Sputum Culture, AFB
- Culture, Sputum, AFB
- Mycobacteria Culture, Sputum
- TB Culture, Sputum
- Acid Fast Bacilli Culture, Sputum
Specimen Requirements
The patient should be instructed to remove dentures, if applicable, rinse mouth woth water and cough deeply, expectorating sputum inot tohe sputum collection cup. First morning sputum yields best recovery of AFB. For optimum recovery, send immediately. If specimen must be stored, refrigerate immediatley upon collection, up to 24 hours; do not incubate. Specify specimen surce, date and time of collection, current antibiotic therapy, and clinical diagnosis. Do not submit more than 4 specimens in one 7 day period unless by prior arrangement. If unacceptable specimens are received,the clinician/client will be notified and another specimen requested before disposal of specimen.
The patient should be instructed to remove dentures, rinse mouth with water and cough deeply, expectorating sputum into the sputum collection cup. First morning sputum yields best recovery of AFB. For optimum recovery, send immediately. If specimen must be stored, refrigerate immediately after specimen collection; do not incubate. May be refrigerated up to 24 hrs. Specify specimen source, collection date/time, current antibiotic therapy, and clinical diagnosis. Do not submit more than four specimens in one 7 day period unless by prior arrangement. If an unacceptable specimen is received, the client will be notified and another specimen will be requested before disposal of the specimen.
5 mL sputum. Low volume sputums will be held up to 7 days and pooled with subsequent specimens until minimum volume is met.
5 mL sputum. Low volume sputums will be held up to 7 days and pooled with subsequent specimens until minimum volume is met.
Additional Information
Test includes culture, acid-fast smear and concentration of specimen. Recommended screening procedure is 3 first morning specimens of adequate volume submitted on 3 consecutive days. If the acid-fast smear is positive, the Mycobacterium tuberculosis molecular detection PCR, Respiratory, will be performed automatically at an additional charge. Test includes identification of organisms and susceptibility testing of potentially pathogenic organism(s) at an additional charge unless specifically declined. Susceptibilities are performed on the first organism isolated from a patient and at 2-6 month intervals if that organism continues to be isolated while the patient is on therapy. Mycobacterium tuberculosis organism ID and susceptibility testing is sent to the Michigan Department of Health & Human Services (MDHHS); although there is no charge for testing, MLabs charges a handling fee for processing and forwarding specimens to MDHHS. Non-tuberculosis susceptibility testing is sent to Mayo Medical Laboratories. A subculture of the isolate is kept for 1 year by the Microbiology Laboratory for further testing, if necessary. By ordering this test the clinician acknowledges that additional reflex testing will be performed and billed at a separate additional charge if indicated.