What is sputum? 

Sputum is lower respiratory tract secretions expelled by coughing (not saliva). Its characteristics can give important clues about pulmonary and systemic disease. 

Key Components of Sputum Assessment 

1. Amount:

Scanty: early infection, asthma 
Copious: bronchiectasis, lung abscess, pulmonary oedema 
Sudden large volume: ruptured lung abscess into bronchus 

2. Colour (General principles): 
 


3. Consistency 
Mucoid: asthma, chronic bronchitis 
Purulent: bacterial infection 
Frothy: pulmonary oedema 
Thick, tenacious: cystic fibrosis, asthma 

4. Odour 
Foul-smelling: anaerobic infection, lung abscess, aspiration pneumonia 

5. Presence of Blood (Haemoptysis)
Small streaks: bronchitis, pneumonia 
Large volumes: TB, lung cancer, bronchiectasis, PE 
Always distinguish from haematemesis or epistaxis 

Microscopic Examination:

Cells:
Neutrophils: bacterial infection 
Eosinophils: asthma, parasitic infection 
Macrophages: chronic lung disease 
Hemosiderin-laden macrophages: pulmonary haemorrhage 
Lipid-laden macrophages: aspiration 

Organisms 
Gram stain: bacteria 
Ziehl–Neelsen stain: Acid-fast bacilli (TB) 
Silver stain: Pneumocystis jirovecii 
Fungal elements: hyphae or yeast 

Crystals & Special Findings:

Sputum Culture & Sensitivity 

Indicated in: 

Severe pneumonia 
TB suspicion 
Non-resolving infection 

Good-quality sputum: 
Few epithelial cells 
Many neutrophils 

Commonly: 

Rust-coloured sputum → Strep. pneumoniae 
Pink frothy sputum → Pulmonary oedema 
Foul-smelling sputum → Anaerobes 
Early morning sputum → best for TB testing 

Key points: 

Always describe sputum systematically: 
Amount → Colour → Consistency → Odour → Blood → Duration