Investigators will enroll prospectively all clinically and radiologically suspected tuberculosis patients from 20 to 29 years old who visited the Armed Forces Capital Hospital. Investigators will perform QFT and tuberculin skin test. Diagnosis of tuberculosis will be made by World Health Organization guideline and the physician will not know the QuantiFERON-TB Gold in-tube results before the diagnosis and anti-tuberculosis medication. Investigators will evaluate the sensitivity and specificity of QuantiFERON-TB Gold in-tube in the diagnosis of active tuberculosis among young adults.