Diagnosis of TB should be considered with symptoms lasting longer than 2 weeks. A multiple sputum cultures for acid-fast bacilli and chest X-ray are typically part of the initial assessment. Tuberculin skin tests and Interferon-? release assays are generally used in developing countries. TB diagnosis is made by identifying M. tuberculosis in a clinical sample such as pus, sputum, blood, or tissue biopsy. This slow-growing organism can take two to six weeks for sputum or blood cultures for their process. Hence, treatment is often begun before results of cultures are confirmed. Adenosine deaminase testing and Nucleic acid amplification tests may allow rapid diagnosis of Tuberculosis, these tests are not regularly recommended. Blood tests to detect antibodies are not very sensitive or specific so they are not recommended.
The Mantoux tuberculin skin test is often used to test people at high risk of Tuberculosis. People who have been earlier immunized may have a false-positive result. The test may be detected falsely negative in those people with malnutrition, Hodgkin's lymphoma, sarcoidosis, and mostly in, active TB. Those who are positive to the Mantoux test, interferon-? release assays (IGRAs), on a blood sample, including the QuantiFERON-TB Gold tests (Cellestis) and T-SPOT, are recommended. Most environmental mycobacteria are not affected by immunization so they generate fewer false-positive results. Yet, they are affected by M. szulgai, M. marinum, and M. kansasii. Culture- acid fast detection (Ziel Nielson stain)