Sputum is matter that is expectorated from the respiratory tract, such as mucus or phlegm, mixed with saliva, which can then be spat from the mouth. It is usually associated with air passages in diseased lungs, bronchi, or upper respiratory tract. A sputum sample is the name given to the mucus that is coughed up from the lower airways. It is usually used for microbiological investigations of respiratory infections. The...