Sputum

Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). It is commonly referred to as "phlegm". In medicine, sputum samples are usually used for a naked-eye examination, microbiological investigation of respiratory infections, and cytological investigations of respiratory system.

These naked-eye examinations have been found to be successful, but are subjective to the examiner (in a professional setting, a clinician). Current technologies exist that can analyze sputum more objectively, but are often expensive, complex, or difficult to use.

A naked eye exam of the sputum can be done at home by a patient in order to note the various colors (see below). Any hint of yellow or green color (pus) suggests an airway infection (but does not indicate the type of organism causing it). Such color hints are best detected when the sputum is viewed against a bright white background, such as white paper, a white pot, or a white sink surface.

Having green, yellow, or thickened phlegm (sputum) does not always indicate the presence of an infection. Also, if an infection is present, the color of the phlegm (sputum) does not determine whether a virus, a bacterium or another pathogen has caused it. Simple allergies can also cause changes in the color of mucus.