Whether a negative TB test is normal or not depends largely on which type of TB negative is being tested for. If the tuberculin test is negative, it suggests that tuberculin is not present in the body and there is no tuberculosis infection. In addition, taking secretions from the respiratory tract, such as sputum, and looking for or culturing Mycobacterium tuberculosis with negative results can only suggest that there is no infectiousness in the body, no active stage of tuberculosis, and may also suggest that there is no tuberculosis infection. In order to determine whether or not there is tuberculosis infection, it is necessary to combine the tuberculin test with X-rays of both lungs, CT or MRI, bronchial fiberoptic endoscopy if necessary, and biopsy, searching for or culturing of Mycobacterium tuberculosis for a definitive diagnosis, in order to determine whether or not the negative result is normal.