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Sputum may be described as serous, mucoid, mucopurulent or purulent and rust-coloured.

Serous sputum is clear, watery or frothy and may be pink coloured. This is usually due to acute pulmonary oedema but occasionally it occurs in lung cancer.

Rusty sputum occurs in pneumococcal (lobar) pneumonia.

Mucoid sputum is clear, white or grey and occurs in asthma and chronic bronchitis and in acute viral respiratory infections before secondary bacterial infection ensues. Drying of mucoid sputum during asthma attacks makes the sputum stringy in consistency, even forming casts.

Mucopurulent or purulent sputum may be yellow green or brown and is seen in all types of bronchopulmonary infection. Eosinophils can make sputum look purulent.

Last reviewed 01/2018