A number of respiratory diseases can be detected clinically by testing sputum. In particular, inflammatory reactions of the respiratory system, such as tracheitis, bronchitis, and pneumonia due to infection by pathogens such as bacteria and viruses, can clarify the type of pathogen and provide targeted anti-causal treatment. Yellow pus-colored sputum can be seen in Staphylococcus aureus pneumonia, green purulent sputum can be seen in Pseudomonas aeruginosa infection, and rust-colored sputum can be seen in lobar pneumonia. These sputum can be searched for the appropriate pathogens or have pathogen cultures and drug sensitivity tests done to clarify the condition. In addition, cancer cells can be identified to rule out possible lung cancer, and Mycobacterium tuberculosis can be identified to rule out tuberculosis infection.