Diagnosis of tuberculosis (TB) is difficult, since symptoms are often very 
unspecific or lacking. However active, prompt and accurate diagnosis is the key 
element in the public health response to tuberculosis and the cornerstone of 
tuberculosis control. Different diagnostic methods for an assured diagnosis of 
TB are necessary. Chest radiography is a useful keystone to identify 
tuberculosis, but diagnosis of tuberculosis cannot be established by radiography 
alone. CT scanning is used in patients without pathological chest radiography 
but clinically suspected active TB and to differentiate TB from other diseases. 
Radiological appearance is primarily determined by the immune status of patients 
and caverns and disseminated disease foci are often observed. Laboratory 
diagnostic methods include microscopic identification of acid-fast mycobacteria 
from any body fluid (especially sputum), as well as isolation and 
characterisation of mycobacteria in culture. It is then possible to type the 
pathogens by the shape of their colony, their growth behavior and their 
biochemical characteristics. These methods are regarded as the gold standard in 
diagnosis of active TB. In patients who are highly suspected of having TB, but 
whose sputum specimens tested negative for mycobacteria, a nucleic acid 
amplification test is additionally performed. Moreover, sensitivity testing with 
first and second line antitubercular drugs is applied as standard. Laboratory 
diagnostic testing of cellular immunity against pathogenic mycobacteria employs 
the tuberculin skin test (TST, Mantoux tuberculin test) or the more specific 
interferon γ test to determine γ interferon released by T lymphocytes stimulated 
in vitro. The new ELISA and ELISPOT procedures exhibit higher test specificity 
and less cross reactivity to NTM (non-tuberculosis mycobacteria), are 
independent of BCG-vaccination status and correlate better with the degree of 
exposure than does the TST.