Test Catalog

Test ID: CTBBL    
Mycobacterial Culture, Blood

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosing mycobacteremia

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

When this test is ordered, the reflex tests may be performed and charged.

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 42 days of incubation.

Interpretation Provides information to assist in interpretation of the test results

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.


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.

Supportive Data

During validation of this test, a variety of mycobacteria were recovered from 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 Recommendations for in-depth reading of a clinical nature

1. Pfyffer GE: Mycobacterium: General characteristics, laboratory detection, and staining procedures. In Manual of Clinical Microbiology. Eleventh edition. Edited by JH Jorgensen, MA Pfaller, KC Carroll, et al. ASM Press, Washington DC, 2015, pp 536-569

2. Reimer LG: Laboratory detection of mycobacteremia. Clin Lab Med 1994;14:99-105