Mycobacterial Culture, Blood
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Mycobacteremia occurs most often in immunocompromised hosts. The majority of disseminated mycobacterial infections are due to Mycobacterium avium complex but bacteremia can also be caused by other mycobacterial species including, but not limited to, Mycobacterium tuberculosis complex, Mycobacterium kansasii, Mycobacterium fortuitum, Mycobacterium chelonae, Mycobacterium scrofulaceum, Mycobacterium szulgai, and Mycobacterium xenopi.(1)
Mycobacterial blood cultures may be indicated for patients presenting with signs and symptoms of sepsis, especially fever of unknown origin.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
If positive, mycobacteria is identified.
A final negative report will be issued after 60 days of incubation.
A positive result may support the diagnosis of mycobacteremia.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Results must be interpreted in conjunction with the patient's history and clinical picture because false-positive results may occur due to specimen contamination.
A negative result does not rule-out mycobacteremia. The organism may be present at quantities below the limit of detection or may be transiently present.
If Mycobacterium genavense is suspected, indicate on request form or contact laboratory. Mycobactin J (an iron supplement) will then be added to the culture to support growth.
Mayo isolation rate of mycobacteria from 1995 to 1998 from 172,928 blood cultures was 0.01% (20 positive cultures from 12 patients).
During validation of this test at Mayo, a variety of mycobacteria were recovered from artificially spiked blood specimens. These mycobacteria were Mycobacterium fortuitum, Mycobacterium intracellulare, Mycobacterium kansasii, Mycobacterium tuberculosis, and Mycobacterium xenopi. Mycobacterium genavense was recovered when the medium was supplemented with mycobactin J (an iron supplement). In addition, aerobic actinomycetes including Nocardia farcinica, Gordonia terrae, Rhodococcus equi, and Tsukamurella paurometabola were also recovered when spiked into blood. The limit of detection was determined to be < or =10(2) colony forming units (CFU)/mL for Mycobacterium fortuitum and Mycobacterium tuberculosis, 10 CFU/mL for Mycobacterium intracellulare, and 1 CFU/mL for Nocardia farcinica.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Pfyffer GE: Mycobacterium: General characteristics, laboratory detection, and staining procedures. In Manual of Clinical Microbiology. Ninth edition. Edited by PR Murray, EJ Baron, JH Jorgensen, et al. ASM Press, Washington DC, 2007, pp 543-572
2. Reimer LG. Laboratory detection of mycobacteremia. Clin Lab Med 1994;14:99-105