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- General: Blood and bone marrow cultures are the most sensitive diagnostic tests for MAC. Since bone marrow cultures are more invasive a blood culture is the standard diagnostic procedure.
- Blood culture: A sample of blood is placed in a special laboratory preparation, and then it is incubated in a controlled environment for one to two weeks. A positive culture will identify the disease–causing bacteria.
- Bone marrow culture: A bone marrow culture is an invasive procedure. Therefore, it is only used when all other tests are negative, but the doctor suspects MAC. First a bone marrow biopsy is performed to obtain a tissue sample. During the procedure a needle is inserted into the marrow and a small sample is removed. It is then placed in a special laboratory preparation and incubated in a controlled environment for one to two weeks. A positive culture will identify the disease–causing bacteria.
- Sputum–induction for histopathologic testing: A sputum sample analysis can be conducted to determine whether a patient has MAC. The patient will cough deeply, expelling material that comes up from the lungs into a sterile cup. The sample is then taken to a laboratory and placed in a medium under conditions that allow the bacteria to grow. Mycobacterial cultures grow MAC in about one to two weeks. However, interpreting the results may be difficult because MAC can colonize the respiratory tract without causing clinical infection. A positive culture will identify the disease–causing bacteria. Sensitivity of a sputum analysis varies widely (50–90%), and depends on proficiency in using the technique and the experience of the laboratory.
- Imaging studies: High resolution computed tomography (HRCT) scanning has been shown to be more sensitive than chest radiography (X–ray) for revealing pulmonary abnormalities associated with MAC infection. An HRCT scan of the abdomen may reveal retroperitoneal lymphadenopathy (enlarged lymph nodes near the tissues in the abdominal wall) periaortic lymphadenopathy (enlarged lymph nodes around the aorta) and hepatosplenomegaly (enlarged liver and spleen).
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