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Mycobacteriology Frequently Asked Questions
Q: What are the turnaround times for your testing?
A: Smear and GeneXpert results (NAA) are sent out within 24 hours of receipt of specimen, Monday through Friday. Usually, specimens received before 10 AM can have a smear and GeneXpert result available the same day. Drug susceptibility results are usually sent out within 17 days of a positive M. tb complex culture. Final negative culture results are usually sent out 7 weeks after receipt of specimen.
Q: What anticoagulants are acceptable for Mycobacterial blood culture?
A: Sodium heparin is preferred. SPS is also acceptable.
Q: What type of container should specimens for smear and culture be transported in? Are there any special transport conditions?
A: A 50 mL centrifuge tube is preferred, but any sterile leakproof container is acceptable. Specimens should be refrigerated as much as possible during storage and transport.
Q: What types of specimens can be submitted for GeneXpert (NAA)?
A: Respiratory fluids, such as sputum, trach aspirate, or bronch wash, may be submitted. Please indicate if the specimen has already been decontaminated and concentrated prior to submission on the lab slip. All types of tissue specimen (lung tissue, lymph, node, etc.) are also acceptable.
Q: When can a GeneXpert
A: Any time a patient has been on treatment less than three days and the specimen has been decontaminated within the past week.
Q: Can a GeneXpert be done on a smear-negative specimen?
A: Yes. Please call the lab at (443)681-3942 to request that GeneXpert be performed regardless of smear result. Please be aware that the possibility of a false negative result increases for smear-negative specimens.
Q: Does the lab perform the MTD test?
A: No, the lab performs the GeneXpert, which is an NAA with equivalent performance characteristics to the MTD assay.
Q: What’s the difference between a GeneXpert test and a DNA probe?
The GeneXpert is a nucleic acid amplification assay for the detection of M. tb complex directly from patient specimens. A DNA Probe is an identification technique which requires an isolate of Mycobacteria, and can be used to identify M. tb complex, M. avium complex, M. gordonae, and M. kansasii.
Q: How long does a culture take to grow?
A: This depends on a lot of factors, including bacillary load of specimen and species of Mycobacteria in question.
2 to 4 weeks is the average time, but this may vary.
Q: When is drug susceptibility testing performed?
A: All first isolates of M. tb complex are automatically tested for drug sensitivity. Resistant isolates are retested every two months and sensitive isolates every three months until culture conversion. The lab currently does not perform any susceptibility testing on nontuberculous Mycobacteria.
Q: What drugs are tested for susceptibility?
A: First-line panel includes Streptomycin, INH, Rifampin, Ethambutol, and PZA. Second-line drugs tested are Kanamycin, Ethionamide, PAS, and Ofloxacin.
Q: How long are isolates of Mycobacteria held at your laboratory?
A: Isolates are available for approximately one year after specimen submission, and can be returned to a submitter if additional testing not performed at our lab is required.
Q: How do I access genotyping results?
A: Genotyping results are only provided through out State TB Control Program at (410)767-6698.
Q: How can I get Quantiferon testing done through the State Lab?
A: Quantiferon testing is only performed through a local health department. Contact the local health department in your jurisdiction for further information.
1770 Ashland Ave, Baltimore, MD 21205