1. What is sputum?
Sputum -also known as phlegm – is a mixture of saliva and mucus produced in the lower airways (trachea, bronchi and bronchioles) of the respiratory tract. It is coughed up from the respiratory tract, often during illness.
It is different from saliva alone, which is produced in the mouth.
2. Composition
Sputum typically contains saliva, mucus, cells (like white blood cells, epithelial cells), microorganisms (bacteria, viruses, fungi), and sometimes pus or blood.
3. Function
The primary function of sputum is to trap and remove foreign substances from the respiratory tract. It works with small structures called cilia to move these substances out of the lungs.
The thickness of sputum helps trap germs, and tiny hairs in the airways called cilia push it up to the mouth so it can be coughed out.
4. Colour
- Clear or white. Normal or indicative of viral infection
- Yellow or green. Often suggests a bacterial infection
- Brown, black or rust-colored. Can be associated with old blood, smoking, chronic bronchitis (COPD), or pneumonia
- Pink or red. May indicate the presence of fresh blood, potentially due to tuberculosis, lung cancer, pulmonary embolism – or heart failure (rarely, and may be frothy)
5. Diagnostic tool
Sputum analysis can help diagnose respiratory conditions. Laboratory tests such as sputum culture, Gram stain, or acid-fast bacillus (AFB) testing are used to identify infections like tuberculosis.
6. Volume and viscosity
Volume
The amount of sputum produced can vary. Large volumes may suggest chronic lung conditions like bronchiectasis or chronic obstructive pulmonary disease (COPD).
Viscosity
The thickness of sputum can indicate the severity of an illness. Thick, sticky sputum might be seen in conditions like cystic fibrosis, while watery sputum is often linked to viral infection.
7. Foul-smelling sputum
This can be a sign of lung abscesses, bronchiectasis, or anaerobic bacterial infections.
8. Increased sputum production triggers
Common causes of increased sputum production include infection (e.g., pneumonia, bronchitis), chronic lung diseases (exacerbation of COPD), smoking, and environmental irritants.
9. Role in disease progression
In conditions like COPD, frequent coughing up of sputum is a symptom of disease progression and worsening lung function.
10. Management
Treatment of sputum production involves addressing the underlying condition. This may include antibiotics for bacterial infections, bronchodilators, and expectorants to help clear mucus from the lungs. In some cases, hydration and humidification can also assist in managing symptoms.
Summary
We have described 10 facts about sputum (phlegm). We hope it has been helpful.
Other resources
Review article: Shen, 2023
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