Sputum ['spju.təm] is mucus and is the name used for the coughed-up material (phlegm) from the lower airways (trachea and bronchi). This process is known as sputilization. In medicine, sputum samples are usually used for naked eye (gross) exam, microbiological investigations of respiratory infections and cytological investigations of respiratory systems. It is critical that the patient not give a specimen that includes any mucoid material from the interior of the nose. Naked eye exam of sputum can be done at home by a patient in order to note the various colors (see below). Any hint of yellow color suggests an airway infection (but does not indicate between the types of organisms causing it). Such color hints are best detected when the sputum is viewed on a very white background such as white paper, a white pot, or a white sink surface. The more intense the yellow color, the more likely it is a bacterial infection (bronchitis, bronchopneumonia, or pneumonia).