Abnormal sputum
Other namesMucus
Cocci-shaped Enterococcus sp. bacteria taken from a pneumonia patient
  • /'spju:təm/
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Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked eye examination, microbiological investigation of respiratory infections and cytological investigations of respiratory systems. It is crucial that the specimen does not include any mucoid material from the nose or oral cavity.

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 on a very 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 the mucus. [1]


The best sputum samples contain very little saliva,[2] as saliva contaminates the sample with oral bacteria. This is especially true for samples for laboratory testing in cytology or microbiology. Specimen adequacy is assessed by the laboratory technologists by examining a Gram stain or cytology stain of the sputum. More than 25 squamous epithelial cells at low power magnification exam under the microscope strongly suggest salivary contamination.[3] Sputum samples have been used to quantify the degree of airway inflammation in human diseases such as asthma. Specifically, this work has demonstrated that a subgroup of severe asthma patients has airway inflammation that is resistant to treatment with corticosteroids.[4]

When a sputum specimen is plated out in microbiology, it is best to get the portion of the sample that almost looks like yellow pus onto the swab. If there is any blood in the sputum, this should also be on the swab.[citation needed] Microbiological sputum samples are used to look for infections, such as Moraxella catarrhalis, Mycobacterium tuberculosis, Streptococcus pneumoniae, and Haemophilus influenzae. Other pathogens can also be found.

Purulent sputum[5] contains pus, composed of white blood cells, cellular debris, dead tissue, serous fluid, and viscous liquid (mucus). Purulent sputum is typically yellow or green. It is seen in cases of pneumonia, bronchiectasis, lung abscess, or an advanced stage of bronchitis.[6]


Sputum can be (when examined by the naked eye):[citation needed]

See also


  1. ^ "Green phlegm and snot 'not always a sign of an infection needing antibiotics'". GOV.UK. 18 November 2013. Retrieved 2022-04-17.
  2. ^ Clinical Microbiology procedures handbook, American Society for Microbiology 2nd Ed. 2007 update
  3. ^ Gershman, Neil H.; Liu, Hong; Wong, Hofer H.; Liu, Jane T.; Fahy, John V. (August 1999). "Fractional analysis of sequential induced sputum samples during sputum induction: Evidence that different lung compartments are sampled at different time points". Journal of Allergy and Clinical Immunology. 104 (2): 322–328. doi:10.1016/S0091-6749(99)70374-X. PMID 10452752.
  4. ^ Peters, Michael C.; Kerr, Sheena; Dunican, Eleanor M.; Woodruff, Prescott G.; Fajt, Merritt L.; Levy, Bruce D.; Israel, Elliot; Phillips, Brenda R.; Mauger, David T.; Comhair, Suzy A.; Erzurum, Serpil C.; Johansson, Mats W.; Jarjour, Nizar N.; Coverstone, Andrea M.; Castro, Mario; Hastie, Annette T.; Bleecker, Eugene R.; Wenzel, Sally E.; Fahy, John V. (March 2018). "Refractory airway type 2 inflammation in a large subgroup of asthmatic patients treated with inhaled corticosteroids". Journal of Allergy and Clinical Immunology. 143 (1): 104–113.e14. doi:10.1016/j.jaci.2017.12.1009. PMC 6128784. PMID 29524537.
  5. ^ a b Richard F. LeBlond; Richard L. DeGowin; Donald E. Brown (2004). DeGowin's diagnostic examination. New York: McGraw-Hill. ISBN 0-07-140923-8.
  6. ^ What can sputum tell us?
  7. ^ Altiner A, Wilm S, Däubener W, Bormann C, Pentzek M, Abholz HH, Scherer M (2009). "Sputum color for diagnosis of a bacterial infection in patients with acute cough". Scand J Prim Health Care. 27 (2): 70–3. doi:10.1080/02813430902759663. PMC 3410464. PMID 19242860.
  8. ^ Sputum Color is the Key to Treating Acute COPD Exacerbations