Latent tuberculosis is diagnosed by a skin test or a blood test. It is a measure of immunity against Mycobacterium tuberculosis. 

Active tuberculosis, on the other hand, is diagnosed by sending body fluid / tissue samples (e.g. blood, sputum, or body tissue) to the laboratory to be incubated. The diagnosis of active tuberculosis is confirmed when the incubated samples are found to positive for growth of Mycobacterium tuberculosis. This process may take up to 2 months as it is a slow growing organism. Nowadays, modern technology such as DNA testing has allowed for easier and more rapid diagnosis. Nonetheless, the diagnosis of active tuberculosis infection can remain difficult and all the available testing methods may still yield a negative result. In such cases, the diagnosis and management depends very much on the clinical acumen and judgement of the physician.