A negative sputum culture means that no pathogenic bacteria have been cultured in the sputum. Negative sputum culture with shadows on the lungs may be due to tuberculosis, or it may be due to pneumonia or lung tumor. 1. Tuberculosis: Mycobacterium tuberculosis is a kind of bacteria that is hard to be cultured, so tuberculosis may have negative sputum culture. And the active stage of tuberculosis can be manifested by the condition of having shadows in the lungs. Therefore, sputum culture negative lungs with shadows may be tuberculosis, but not necessarily tuberculosis. 2. Pneumonia: Due to the error of test results, negative sputum culture results may also occur in pneumonia. Pneumonia will cause some damage to the lungs, so there will be shadows in the lungs when taking radiographs. 3. Lung tumor: sputum culture can only detect tuberculin and bacterial infections, so lung tumor, sputum culture results are often negative, due to the emergence of substantial tumors often appear in the lungs with shadows. In case of negative sputum culture with shadows on the lungs, it is necessary to do further examination according to the doctor’s instruction to clarify the specific cause and then carry out targeted treatment.